diff --git a/kadai2/kynefuk/.gitignore b/kadai2/kynefuk/.gitignore
new file mode 100644
index 0000000..05ecac4
--- /dev/null
+++ b/kadai2/kynefuk/.gitignore
@@ -0,0 +1,27 @@
+# Created by https://www.toptal.com/developers/gitignore/api/go
+# Edit at https://www.toptal.com/developers/gitignore?templates=go
+
+### Go ###
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+### Go Patch ###
+/vendor/
+/Godeps/
+
+img
+
+# End of https://www.toptal.com/developers/gitign
\ No newline at end of file
diff --git a/kadai2/kynefuk/README.md b/kadai2/kynefuk/README.md
new file mode 100644
index 0000000..2c9bb7b
--- /dev/null
+++ b/kadai2/kynefuk/README.md
@@ -0,0 +1,40 @@
+# <課題 2> io.Reader と io.Writer
+
+### io.Reader とは
+
+一連のデータ(バイト列)の読み込み処理を抽象化したインターフェース。
+読み込まれる対象データとしてバイト型の配列を受け取り、読み込んだバイト数とエラーを戻り値とする。
+
+```
+type Reader interface {
+    Read(p []byte) (n int, err error)
+}
+```
+
+### io.Writer とは
+
+一連のデータ(バイト列)の書き込み処理を抽象化したインターフェース
+書き込まれる対象データとしてバイト型の配列を受け取り、書き込んだバイト数とエラーを戻り値とする。
+
+```
+type Writer interface {
+    Write(p []byte) (n int, err error)
+}
+```
+
+## 標準パッケージでどのように使われているか
+
+データの入出力を表現する様々なパッケージで io.Reader や io.Writer が実装している。
+(標準入力を表す`os.Stdin`、標準出力を表す`os.Stdout`、ファイルの入出力を表現する`os.File`や、通信の入出力を表現する`net.Conn`など)
+
+## io.Reader と io.Writer があることでどういう利点があるのか具体例を挙げて考えてみる
+
+入力処理と出力処理の仕様をインターフェースとして定義しておくことで、様々な入出力処理を統一的に扱うことができ、プログラムの柔軟性が高くなる。
+例えば、何らかの読み込み処理を行う関数の引数の型を`io.Reader`とすることで、`io.Reader`を実装している型であれば何でも受けることができる。
+コマンドラインのの処理内容を出力する標準出力や、エラーを表示する標準エラー出力のフィールドの型として io.Writer を指定することで、テスト時に、`bytes.Buffer`などに切り替えることができ、テスト容易性を高めることができる。
+
+```
+type Command struct {
+	OutStream, ErrStream io.Writer
+}
+```
diff --git a/kadai2/kynefuk/cli/args.go b/kadai2/kynefuk/cli/args.go
new file mode 100644
index 0000000..5a9dcbb
--- /dev/null
+++ b/kadai2/kynefuk/cli/args.go
@@ -0,0 +1,44 @@
+package cli
+
+import (
+	"fmt"
+)
+
+// Args represents CLI's arguments object
+type Args struct {
+	DirecTory, From, To string
+}
+
+// Validate is a validation method
+func (args *Args) Validate() error {
+	fileExtMap := createFileExtMap()
+	if _, ok := fileExtMap[args.From]; !ok {
+		return fmt.Errorf("argument of \"-f, --From\" is not valid file format. invalid format: %s", args.From)
+	}
+	if _, ok := fileExtMap[args.To]; !ok {
+		return fmt.Errorf("argument of \"-t, --To\" is not valid file format. invalid format: %s", args.To)
+	}
+
+	return nil
+}
+
+func createFileExtMap() map[string]string {
+	fileExtMap := make(map[string]string)
+	list := []string{
+		"jpg",
+		"jpeg",
+		"png",
+		"gif",
+		"bmp",
+		"tiff",
+	}
+	for _, v := range list {
+		fileExtMap[v] = ""
+	}
+	return fileExtMap
+}
+
+// NewArgs is a construcTor of Args
+func NewArgs(DirecTory, From, To string) *Args {
+	return &Args{DirecTory: DirecTory, From: From, To: To}
+}
diff --git a/kadai2/kynefuk/cli/args_test.go b/kadai2/kynefuk/cli/args_test.go
new file mode 100644
index 0000000..c4220f7
--- /dev/null
+++ b/kadai2/kynefuk/cli/args_test.go
@@ -0,0 +1,31 @@
+package cli
+
+import (
+	"testing"
+
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/helper"
+)
+
+const dummyDir = "dummy"
+
+func TestArgs(t *testing.T) {
+	cases := []struct{ name, fromFormat, toFormat, expectedMessage string }{
+		{name: "valid arguments", fromFormat: "jpeg", toFormat: "png", expectedMessage: ""},
+		{name: "invalid from format", fromFormat: "hoge", toFormat: "jpg", expectedMessage: "argument of \"-f, --From\" is not valid file format. invalid format: hoge"},
+		{name: "invalid to format", fromFormat: "gif", toFormat: "hage", expectedMessage: "argument of \"-t, --To\" is not valid file format. invalid format: hage"},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			args := NewArgs(dummyDir, c.fromFormat, c.toFormat)
+			actual := args.Validate()
+			if actual == nil {
+				if c.expectedMessage != "" {
+					helper.ErrorHelper(t, actual, c.expectedMessage)
+				}
+			} else if actual.Error() != c.expectedMessage {
+				helper.ErrorHelper(t, actual, c.expectedMessage)
+			}
+		})
+	}
+}
diff --git a/kadai2/kynefuk/cli/cli.go b/kadai2/kynefuk/cli/cli.go
new file mode 100644
index 0000000..de244d1
--- /dev/null
+++ b/kadai2/kynefuk/cli/cli.go
@@ -0,0 +1,45 @@
+package cli
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/converter"
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/walker"
+)
+
+// it represents Exit Code
+const (
+	ExitCodeOK = iota
+	ExitCodeError
+)
+
+// Command represents CLI object
+type Command struct {
+	OutStream, ErrStream io.Writer
+}
+
+// Run invoke cli main logic
+func (cli *Command) Run(directory, from, to string) int {
+	dirWalker := walker.NewWalker(from)
+	files, err := dirWalker.Dirwalk(directory)
+	if err != nil {
+		fmt.Fprintf(cli.ErrStream, "failed to read directory: %s, err: %s\n", directory, err)
+		return ExitCodeError
+	}
+
+	imgConverter := converter.NewConverter(from, to)
+	for _, file := range files {
+		dstPath := converter.ConvertExt(file, from, to)
+		if err := imgConverter.ConvertFormat(file, dstPath); err != nil {
+			fmt.Fprintf(cli.ErrStream, "failed to convert img, err: %s\n", err)
+			return ExitCodeError
+		}
+	}
+	return ExitCodeOK
+}
+
+// NewCommand is a constructor of CLI
+func NewCommand(outStream, errStream io.Writer) *Command {
+	return &Command{OutStream: outStream, ErrStream: errStream}
+}
diff --git a/kadai2/kynefuk/cli/cli_test.go b/kadai2/kynefuk/cli/cli_test.go
new file mode 100644
index 0000000..5ded4c4
--- /dev/null
+++ b/kadai2/kynefuk/cli/cli_test.go
@@ -0,0 +1,63 @@
+package cli
+
+import (
+	"bytes"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/helper"
+)
+
+var fileExtList = []string{
+	"jpg",
+	"jpeg",
+	"png",
+	"gif",
+	"bmp",
+	"tiff",
+}
+
+func ConvertExt(filepath, to string) string {
+	return strings.Replace(filepath, ".png", to, 1)
+}
+
+func TestCLI(t *testing.T) {
+	testDir := helper.CreateTmpDir()
+	defer os.RemoveAll(testDir)
+	outStream, errStream := new(bytes.Buffer), new(bytes.Buffer)
+	command := NewCommand(outStream, errStream)
+
+	cases := []struct {
+		name       string
+		directory  string
+		fromFormat string
+		toFormat   string
+		outStream  string
+		errStream  string
+		exitCode   int
+	}{
+		{name: "success", directory: testDir, fromFormat: "png", toFormat: "jpg", outStream: "", errStream: "", exitCode: 0},
+		{name: "invalid directory", directory: "dummyDir", fromFormat: "jpg", toFormat: "png", outStream: "", errStream: "failed to read directory: dummyDir, err: open dummyDir: no such file or directory", exitCode: 1},
+		{name: "invalid to format", directory: testDir, fromFormat: "jpg", toFormat: "hoge", outStream: "", errStream: "failed to convert img, err: unknown format type", exitCode: 1},
+		{name: "invalid from format", directory: testDir, fromFormat: "hoge", toFormat: "png", outStream: "", errStream: "", exitCode: 1},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			tmpFile := helper.CreateTmpFile(testDir, c.fromFormat)
+			defer os.Remove(tmpFile.Name())
+			status := command.Run(c.directory, c.fromFormat, c.toFormat)
+
+			if status != c.exitCode {
+				helper.ErrorHelper(t, c.exitCode, status)
+			}
+			if !strings.Contains(outStream.String(), c.outStream) {
+				helper.ErrorHelper(t, c.outStream, outStream.String())
+			}
+			if !strings.Contains(errStream.String(), c.errStream) {
+				helper.ErrorHelper(t, c.errStream, errStream.String())
+			}
+		})
+	}
+}
diff --git a/kadai2/kynefuk/cli/example130541744/example.859397199.jpg b/kadai2/kynefuk/cli/example130541744/example.859397199.jpg
new file mode 100644
index 0000000..02a5c44
Binary files /dev/null and b/kadai2/kynefuk/cli/example130541744/example.859397199.jpg differ
diff --git a/kadai2/kynefuk/cli/example979633815/example.209719562.jpg b/kadai2/kynefuk/cli/example979633815/example.209719562.jpg
new file mode 100644
index 0000000..02a5c44
Binary files /dev/null and b/kadai2/kynefuk/cli/example979633815/example.209719562.jpg differ
diff --git a/kadai2/kynefuk/converter/converter.go b/kadai2/kynefuk/converter/converter.go
new file mode 100644
index 0000000..11c71ab
--- /dev/null
+++ b/kadai2/kynefuk/converter/converter.go
@@ -0,0 +1,66 @@
+package converter
+
+import (
+	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"os"
+	"strings"
+
+	"golang.org/x/image/bmp"
+	"golang.org/x/image/tiff"
+)
+
+// Converter converts image file
+type Converter struct {
+	From, To string
+}
+
+// ConvertFormat converts file format
+func (converter *Converter) ConvertFormat(filepath, dst string) error {
+	file, err := os.Open(filepath)
+	if err != nil {
+		return fmt.Errorf("failed to open file. file: %s", filepath)
+	}
+	defer file.Close()
+
+	img, _, err := image.Decode(file)
+	if err != nil {
+		return fmt.Errorf("failed to decode file. file: %s", filepath)
+	}
+
+	out, err := os.Create(dst)
+	if err != nil {
+		return fmt.Errorf("failed to create output file. file: %s", dst)
+	}
+	defer out.Close()
+
+	switch converter.To {
+	case "jpg", "jpeg":
+		err = jpeg.Encode(out, img, &jpeg.Options{Quality: 100})
+	case "png":
+		err = png.Encode(out, img)
+	case "gif":
+		err = gif.Encode(out, img, &gif.Options{NumColors: 256, Quantizer: nil, Drawer: nil})
+	case "bmp":
+		err = bmp.Encode(out, img)
+	case "tiff":
+		err = tiff.Encode(out, img, nil)
+	default:
+		return fmt.Errorf("unknown format type")
+	}
+
+	return err
+}
+
+// ConvertExt converts file format extention
+func ConvertExt(filepath, from, to string) string {
+	return strings.Replace(filepath, from, to, 1)
+}
+
+// NewConverter is a Constructor of Converter
+func NewConverter(from, to string) *Converter {
+	return &Converter{From: from, To: to}
+}
diff --git a/kadai2/kynefuk/converter/converter_test.go b/kadai2/kynefuk/converter/converter_test.go
new file mode 100644
index 0000000..0b08992
--- /dev/null
+++ b/kadai2/kynefuk/converter/converter_test.go
@@ -0,0 +1,42 @@
+package converter
+
+import (
+	"os"
+
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/helper"
+
+	"testing"
+)
+
+var fileExtList = []string{
+	"jpg",
+	"jpeg",
+	"png",
+	"gif",
+	"bmp",
+	"tiff",
+}
+
+const testDirPath = "../testdata"
+
+func TestConverter(t *testing.T) {
+	tmpDir := helper.CreateTmpDir()
+	defer os.RemoveAll(tmpDir)
+
+	// from→toに画像変換できているかテスト
+	for _, from := range helper.FileExtList {
+		for _, to := range helper.FileExtList {
+			tmpFile := helper.CreateTmpFile(tmpDir, from)
+			defer os.Remove(tmpFile.Name())
+			imgConverter := NewConverter(from, to)
+			err := imgConverter.ConvertFormat(tmpFile.Name(), ConvertExt(tmpFile.Name(), from, to))
+			if err != nil {
+				t.Errorf("failed to test. error: %s", err)
+			}
+			exists := helper.Exists(ConvertExt(tmpFile.Name(), from, to))
+			if !exists {
+				t.Errorf("want true, but got %v", exists)
+			}
+		}
+	}
+}
diff --git a/kadai2/kynefuk/go.mod b/kadai2/kynefuk/go.mod
new file mode 100644
index 0000000..8720123
--- /dev/null
+++ b/kadai2/kynefuk/go.mod
@@ -0,0 +1,5 @@
+module github.com/gopherdojo/dojo8/kadai2/kynefuk
+
+go 1.14
+
+require golang.org/x/image v0.0.0-20200618115811-c13761719519
diff --git a/kadai2/kynefuk/go.sum b/kadai2/kynefuk/go.sum
new file mode 100644
index 0000000..83da957
--- /dev/null
+++ b/kadai2/kynefuk/go.sum
@@ -0,0 +1,4 @@
+github.com/gopherdojo/dojo8 v0.0.0-20200703052727-6a79d18126bf h1:lpYevjFQMxI5VNBc3WXV6Z5pDDrdppdDKwmeBoyt5BE=
+golang.org/x/image v0.0.0-20200618115811-c13761719519 h1:1e2ufUJNM3lCHEY5jIgac/7UTjd6cgJNdatjPdFWf34=
+golang.org/x/image v0.0.0-20200618115811-c13761719519/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
diff --git a/kadai2/kynefuk/helper/helper.go b/kadai2/kynefuk/helper/helper.go
new file mode 100644
index 0000000..232830f
--- /dev/null
+++ b/kadai2/kynefuk/helper/helper.go
@@ -0,0 +1,104 @@
+package helper
+
+import (
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"io/ioutil"
+	"log"
+	"os"
+	"testing"
+
+	"golang.org/x/image/bmp"
+	"golang.org/x/image/tiff"
+)
+
+var FileExtList = []string{
+	"jpg",
+	"jpeg",
+	"png",
+	"gif",
+	"bmp",
+	"tiff",
+}
+
+func CreateTmpDir() string {
+	dir, err := ioutil.TempDir("./", "example")
+	if err != nil {
+		log.Fatalf("failed to create test dir. error: %s", err)
+	}
+	return dir
+}
+
+func CreateJPG(f *os.File, img *image.RGBA) error {
+	return jpeg.Encode(f, img, &jpeg.Options{Quality: 100})
+}
+
+func CreatePNG(f *os.File, img *image.RGBA) error {
+	return png.Encode(f, img)
+}
+
+func CreateGIF(f *os.File, img *image.RGBA) error {
+	return gif.Encode(f, img, &gif.Options{NumColors: 256, Quantizer: nil, Drawer: nil})
+}
+
+func CreateBMP(f *os.File, img *image.RGBA) error {
+	return bmp.Encode(f, img)
+}
+
+func CreateTIFF(f *os.File, img *image.RGBA) error {
+	return tiff.Encode(f, img, nil)
+}
+
+func CreateTmpFile(dir, fileExt string) *os.File {
+
+	img := image.NewRGBA(image.Rect(0, 0, 100, 50))
+
+	f, err := ioutil.TempFile(dir, "example.*."+fileExt)
+	if err != nil {
+		log.Fatalf("failed to create tmp file. error: %s", err)
+	}
+	defer f.Close()
+
+	switch fileExt {
+	case "jpg", "jpeg":
+		err = CreateJPG(f, img)
+	case "png":
+		err = CreatePNG(f, img)
+	case "gif":
+		err = CreateGIF(f, img)
+	case "bmp":
+		err = CreateBMP(f, img)
+	case "tiff":
+		err = CreateTIFF(f, img)
+	}
+
+	if err != nil {
+		log.Fatalf("failed to create test file. fileExt: %s", fileExt)
+	}
+
+	return f
+}
+
+func CreateTmpFiles(dir string) []string {
+	var tmpFilePaths []string
+	for _, v := range FileExtList {
+		f, err := ioutil.TempFile(dir, "example.*."+v)
+		if err != nil {
+			log.Fatalf("failed to create tmp file. error: %s", err)
+		}
+		tmpFilePaths = append(tmpFilePaths, f.Name())
+	}
+	return tmpFilePaths
+}
+
+func Exists(filename string) bool {
+	_, err := os.Stat(filename)
+	return err == nil
+}
+
+func ErrorHelper(tb testing.TB, want, got interface{}) {
+	tb.Helper()
+	tb.Errorf("want = %v, got = %v", want, got)
+}
diff --git a/kadai2/kynefuk/main.go b/kadai2/kynefuk/main.go
new file mode 100644
index 0000000..998d8d3
--- /dev/null
+++ b/kadai2/kynefuk/main.go
@@ -0,0 +1,32 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/cli"
+)
+
+func main() {
+	var directory string
+	var from string
+	var to string
+	flag.StringVar(&directory, "directory", "./", "directory")
+	flag.StringVar(&directory, "d", "./", "directory(short)")
+	flag.StringVar(&from, "from", "jpg", "from format")
+	flag.StringVar(&from, "f", "jpg", "from format(short)")
+	flag.StringVar(&to, "to", "png", "to format")
+	flag.StringVar(&to, "t", "png", "to format(short)")
+	flag.Parse()
+
+	command := cli.NewCommand(os.Stdout, os.Stderr)
+
+	args := cli.NewArgs(directory, from, to)
+	if err := args.Validate(); err != nil {
+		fmt.Fprintf(command.ErrStream, "error: %s\n", err)
+		os.Exit(cli.ExitCodeError)
+	}
+
+	os.Exit(command.Run(args.DirecTory, args.From, args.To))
+}
diff --git a/kadai2/kynefuk/walker/walker.go b/kadai2/kynefuk/walker/walker.go
new file mode 100644
index 0000000..c2c069c
--- /dev/null
+++ b/kadai2/kynefuk/walker/walker.go
@@ -0,0 +1,41 @@
+package walker
+
+import (
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+)
+
+// Walker walk directory to extract files
+type Walker struct {
+	TargetExt string
+}
+
+// Dirwalk walk directory and collect files
+func (walker *Walker) Dirwalk(directory string) ([]string, error) {
+	items, err := ioutil.ReadDir(directory)
+	if err != nil {
+		return nil, err
+	}
+
+	var paths []string
+	for _, item := range items {
+		if item.IsDir() {
+			items, err := walker.Dirwalk(filepath.Join(directory, item.Name()))
+			if err != nil {
+				return nil, err
+			}
+			paths = append(paths, items...)
+			continue
+		}
+		if strings.HasSuffix(item.Name(), walker.TargetExt) {
+			paths = append(paths, filepath.Join(directory, item.Name()))
+		}
+	}
+	return paths, nil
+}
+
+// NewWalker is a constructor of Walker
+func NewWalker(targetExt string) *Walker {
+	return &Walker{TargetExt: targetExt}
+}
diff --git a/kadai2/kynefuk/walker/walker_test.go b/kadai2/kynefuk/walker/walker_test.go
new file mode 100644
index 0000000..ae356a7
--- /dev/null
+++ b/kadai2/kynefuk/walker/walker_test.go
@@ -0,0 +1,50 @@
+package walker
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"testing"
+
+	"github.com/gopherdojo/dojo8/kadai2/kynefuk/helper"
+)
+
+func TestWalker(t *testing.T) {
+	tmpDir := helper.CreateTmpDir()
+	tmpFilePaths := helper.CreateTmpFiles(tmpDir)
+	defer os.RemoveAll(tmpDir)
+
+	type TestCase struct {
+		name, directory, fromFmt string
+		files                    []string
+		err                      error
+	}
+
+	type TestCases []struct {
+		name, directory, fromFmt string
+		files                    []string
+		err                      error
+	}
+
+	var testCases TestCases
+	for _, fileFmt := range helper.FileExtList {
+		name := fmt.Sprintf("walker collects %s file", fileFmt)
+		tests := TestCase{
+			name: name, directory: tmpDir, fromFmt: fileFmt, files: tmpFilePaths, err: nil,
+		}
+		testCases = append(testCases, tests)
+	}
+
+	for _, c := range testCases {
+		t.Run(c.name, func(t *testing.T) {
+			dirWalker := NewWalker(c.fromFmt)
+			files, err := dirWalker.Dirwalk(c.directory)
+			if err != c.err {
+				t.Errorf("test failed. error: %s", err)
+			}
+			if reflect.DeepEqual(c.files, files) {
+				helper.ErrorHelper(t, c.files, files)
+			}
+		})
+	}
+}