diff --git a/kadai2/sminamot/README.md b/kadai2/sminamot/README.md
new file mode 100644
index 0000000..f60f831
--- /dev/null
+++ b/kadai2/sminamot/README.md
@@ -0,0 +1,16 @@
+# 画像変換コマンドの作成
+
+## Usage
+```
+$ ./main [OPTIONS] TARGET_DIR
+```
+OPTIONS
+```
+  -dst string
+        output format (default "png")
+  -src string
+        input format (default "jpg")
+```
+
+## その他
+* "jpg", "png", "gif"のみ対応
diff --git a/kadai2/sminamot/convert/convert.go b/kadai2/sminamot/convert/convert.go
new file mode 100644
index 0000000..50703c3
--- /dev/null
+++ b/kadai2/sminamot/convert/convert.go
@@ -0,0 +1,93 @@
+package convert
+
+import (
+	"errors"
+	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var (
+	ErrWrongInputSrcExtention = errors.New("src extension is wrong")
+	ErrWrongInputDstExtention = errors.New("dst extension is wrong")
+)
+
+// A Conversion represents an conversion object that includes target file paths to convert and input/output formats
+type Conversion struct {
+	Files []string
+	Src   string
+	Dst   string
+}
+
+// New returns a new Conversion that includes target file paths to convert and input/output formats
+func New(dir, src, dst string) (*Conversion, error) {
+	if !validateExtension(src) {
+		return nil, ErrWrongInputSrcExtention
+	}
+	if !validateExtension(dst) {
+		return nil, ErrWrongInputDstExtention
+	}
+
+	files := []string{}
+	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if filepath.Ext(path) == "."+src {
+			files = append(files, path)
+		}
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return &Conversion{
+		Files: files,
+		Src:   src,
+		Dst:   dst,
+	}, nil
+}
+
+func validateExtension(e string) bool {
+	return (e == "jpg" || e == "png" || e == "gif")
+}
+
+func filename(f, src, dst string) string {
+	return strings.TrimSuffix(f, src) + dst
+}
+
+// Convert executes image conversion
+func (c *Conversion) Convert() {
+	for _, v := range c.Files {
+		sf, err := os.Open(v)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			continue
+		}
+		defer sf.Close()
+		img, _, err := image.Decode(sf)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			continue
+		}
+
+		df, err := os.Create(filename(v, c.Src, c.Dst))
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			continue
+		}
+		defer df.Close()
+
+		switch c.Dst {
+		case "jpg":
+			jpeg.Encode(df, img, nil)
+		case "gif":
+			gif.Encode(df, img, nil)
+		case "png":
+			png.Encode(df, img)
+		}
+	}
+}
diff --git a/kadai2/sminamot/convert/convert_test.go b/kadai2/sminamot/convert/convert_test.go
new file mode 100644
index 0000000..5b82dd7
--- /dev/null
+++ b/kadai2/sminamot/convert/convert_test.go
@@ -0,0 +1,112 @@
+package convert
+
+import (
+	"sort"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+type testNewStruct struct {
+	name           string
+	inputDir       string
+	inputSrc       string
+	inputDst       string
+	wantErr        error
+	wantConversion *Conversion
+}
+
+func TestNew(t *testing.T) {
+	tests := []testNewStruct{
+		{
+			name:           "srcが想定外",
+			inputDir:       "./testdata",
+			inputSrc:       "txt",
+			inputDst:       "png",
+			wantErr:        ErrWrongInputSrcExtention,
+			wantConversion: nil,
+		},
+		{
+			name:           "dstが想定外",
+			inputDir:       "./testdata",
+			inputSrc:       "png",
+			inputDst:       "txt",
+			wantErr:        ErrWrongInputDstExtention,
+			wantConversion: nil,
+		},
+		{
+			name:     "png->jpg",
+			inputDir: "./testdata",
+			inputSrc: "png",
+			inputDst: "jpg",
+			wantErr:  nil,
+			wantConversion: &Conversion{
+				Files: []string{"testdata/talks.png", "testdata/subdir/ref.png"},
+				Src:   "png",
+				Dst:   "jpg",
+			},
+		},
+	}
+
+	// sort Files
+	// https://godoc.org/github.com/google/go-cmp/cmp#example-Option--SortedSlice
+	trans := cmp.Transformer("Sort", func(in []string) []string {
+		out := append([]string(nil), in...)
+		sort.Strings(out)
+		return out
+	})
+
+	for _, tt := range tests {
+		testNew(t, tt, trans)
+	}
+}
+
+func testNew(t *testing.T, tt testNewStruct, tr cmp.Option) {
+	t.Helper()
+	ret, err := New(tt.inputDir, tt.inputSrc, tt.inputDst)
+	if err != tt.wantErr {
+		t.Errorf(`%s: New("%s", "%s", "%s") => error:%v, want error: %v`, tt.name, tt.inputDir, tt.inputSrc, tt.inputDst, err, tt.wantErr)
+	}
+	diff := cmp.Diff(ret, tt.wantConversion, tr)
+	if diff != "" {
+		t.Errorf(`%s: New("%s", "%s", "%s"): Conversion diff:%s`, tt.name, tt.inputDir, tt.inputSrc, tt.inputDst, diff)
+	}
+}
+
+func TestValidateExtension(t *testing.T) {
+	tests := []struct {
+		input string
+		want  bool
+	}{
+		{input: "jpg", want: true},
+		{input: "png", want: true},
+		{input: "gif", want: true},
+		{input: "txt", want: false},
+	}
+
+	for _, tt := range tests {
+		ret := validateExtension(tt.input)
+		if ret != tt.want {
+			t.Errorf(`validateExtension("%s") => %v, want %v`, tt.input, ret, tt.want)
+		}
+	}
+}
+
+func TestFilename(t *testing.T) {
+	tests := []struct {
+		inputName string
+		inputSrc  string
+		inputDst  string
+		want      string
+	}{
+		{inputName: "testdata/talks.png", inputSrc: "png", inputDst: "jpg", want: "testdata/talks.jpg"},
+		{inputName: "testdata/subdir/ref.png", inputSrc: "png", inputDst: "gif", want: "testdata/subdir/ref.gif"},
+	}
+
+	for _, tt := range tests {
+		ret := filename(tt.inputName, tt.inputSrc, tt.inputDst)
+		if ret != tt.want {
+			t.Errorf(`filename("%s", "%s", "%s") => %s, want %s`, tt.inputName, tt.inputSrc, tt.inputDst, ret, tt.want)
+		}
+	}
+}
diff --git a/kadai2/sminamot/convert/testdata/fiveyears.jpg b/kadai2/sminamot/convert/testdata/fiveyears.jpg
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index 0000000..df10648
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diff --git a/kadai2/sminamot/convert/testdata/subdir/ref.png b/kadai2/sminamot/convert/testdata/subdir/ref.png
new file mode 100644
index 0000000..0508f6e
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diff --git a/kadai2/sminamot/convert/testdata/talks.png b/kadai2/sminamot/convert/testdata/talks.png
new file mode 100644
index 0000000..589db47
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diff --git a/kadai2/sminamot/main.go b/kadai2/sminamot/main.go
new file mode 100644
index 0000000..e532f4a
--- /dev/null
+++ b/kadai2/sminamot/main.go
@@ -0,0 +1,26 @@
+package main
+
+import (
+	"flag"
+	"log"
+
+	"github.com/sminamot/dojo4/kadai1/sminamot/convert"
+)
+
+func main() {
+	var src, dst string
+
+	flag.StringVar(&src, "src", "jpg", "input format")
+	flag.StringVar(&dst, "dst", "png", "output format")
+	flag.Parse()
+	if len(flag.Args()) == 0 {
+		log.Fatal("need to specify target dir")
+	}
+	dir := flag.Args()[0]
+
+	c, err := convert.New(dir, src, dst)
+	if err != nil {
+		log.Fatal(err)
+	}
+	c.Convert()
+}