diff --git a/.ruby-version b/.ruby-version
index 9cec7165a..f092941a7 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.1.6
+3.2.8
diff --git a/Dockerfile b/Dockerfile
index 2ad7aa075..e0fe18087 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.1.6
+FROM ruby:3.2.8
 
 ENV LANG C.UTF-8
 
diff --git a/Gemfile b/Gemfile
index 6e3c72806..777786543 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,5 @@
 source 'https://rubygems.org'
-ruby '3.1.6'
+ruby '3.2.8'
 
 gem 'bootsnap'
 gem 'pg'
diff --git a/Gemfile.lock b/Gemfile.lock
index 2415b5684..0afd2fd68 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -567,7 +567,7 @@ DEPENDENCIES
   web-console
 
 RUBY VERSION
-   ruby 3.1.6p260
+   ruby 3.2.8p263
 
 BUNDLED WITH
    2.5.19
diff --git a/app/controllers/docs_controller.rb b/app/controllers/docs_controller.rb
index e2a1d4b4d..9cd3b25ab 100644
--- a/app/controllers/docs_controller.rb
+++ b/app/controllers/docs_controller.rb
@@ -15,7 +15,7 @@ def kata
 
   def show
     @doc = Document.new(params[:id])
-    redirect_to root_url unless @doc.exists?
+    redirect_to root_url unless @doc.exist?
 
     if @doc.content.include? "NUM_OF_"
       @doc.content.gsub! "{{ NUM_OF_JAPAN_DOJOS }}",   Dojo.active_dojos_count.to_s
@@ -32,9 +32,9 @@ def show
     if @meta_image.end_with? '.webp'
       # .webp -> .jpg
       # .webp -> .png
-      @meta_image.gsub!('.webp', '.jpg')  if File.exists? "public/#{@meta_image[0..-6]}.jpg"
-      @meta_image.gsub!('.webp', '.jpeg') if File.exists? "public/#{@meta_image[0..-6]}.jpeg"
-      @meta_image.gsub!('.webp', '.png')  if File.exists? "public/#{@meta_image[0..-6]}.png"
+      @meta_image.gsub!('.webp', '.jpg')  if File.exist? "public/#{@meta_image[0..-6]}.jpg"
+      @meta_image.gsub!('.webp', '.jpeg') if File.exist? "public/#{@meta_image[0..-6]}.jpeg"
+      @meta_image.gsub!('.webp', '.png')  if File.exist? "public/#{@meta_image[0..-6]}.png"
     end
 
     # Add here if you want to optimize meta description.
diff --git a/app/models/document.rb b/app/models/document.rb
index 2bac3899c..513fb4d82 100644
--- a/app/models/document.rb
+++ b/app/models/document.rb
@@ -55,13 +55,13 @@ def url
     "#{URL_PATH}/#{self.filename}"
   end
 
-  def exists?
+  def exist?
     return false if path.include? "\u0000"
     Document.all.map(&:filename).include?(filename)
   end
 
   def title
-    return '' unless self.exists?
+    return '' unless self.exist?
     @title ||=
       ActionController::Base.helpers.strip_tags(
         Kramdown::Document.new(self.get_first_paragraph, input: 'GFM').to_html
@@ -69,7 +69,7 @@ def title
   end
 
   def description
-    return '' unless self.exists?
+    return '' unless self.exist?
     @desc ||=
       ActionController::Base.helpers.strip_tags(
         Kramdown::Document.new(self.get_second_paragraph, input: 'GFM').to_html
@@ -80,7 +80,7 @@ def description=(text)
   end
 
   def content
-    @content ||= self.exists? ? File.read(self.path) : ''
+    @content ||= self.exist? ? File.read(self.path) : ''
   end
 
   private
diff --git a/app/models/podcast.rb b/app/models/podcast.rb
index d4add910f..ca6c09126 100644
--- a/app/models/podcast.rb
+++ b/app/models/podcast.rb
@@ -18,10 +18,10 @@ def path
     "#{DIR_PATH}/#{id}.md"
   end
 
-  def exists?(offset: 0)
+  def exist?(offset: 0)
     return false if self.path.include?("\u0000")
     return false if (self.id + offset).zero?
-    File.exists?("#{DIR_PATH}/#{id + offset}.md")
+    File.exist?("#{DIR_PATH}/#{id + offset}.md")
   end
 
   def cover
@@ -30,6 +30,6 @@ def cover
   end
 
   def content
-    exists? ? File.read(path) : ''
+    exist? ? File.read(path) : ''
   end
 end
diff --git a/app/views/podcasts/_navigation.html.erb b/app/views/podcasts/_navigation.html.erb
index 7cd656a23..7115660a1 100644
--- a/app/views/podcasts/_navigation.html.erb
+++ b/app/views/podcasts/_navigation.html.erb
@@ -1,6 +1,6 @@
 <div style="display: table; font-weight: bolder; width: 100%; padding: 10px 10px; background-color:#3870c4;">
   <p class="nav prev">
-    <% if @episode.exists?(offset: -1) %>
+    <% if @episode.exist?(offset: -1) %>
       <%= link_to podcast_path(@episode.id - 1), title: '前のエピソードを見る' do %>
 	&laquo; prev
       <% end %>
@@ -12,7 +12,7 @@
     <%= link_to '目次に戻る'.html_safe, podcasts_path %>
   </p>
   <p class="nav next">
-    <% if @episode.exists?(offset: +1) %>
+    <% if @episode.exist?(offset: +1) %>
       <%= link_to podcast_path(@episode.id + 1), title: '次のエピソードを見る' do %>
 	next &raquo;
       <% end %>
diff --git a/spec/features/podcasts_spec.rb b/spec/features/podcasts_spec.rb
index 786a90eb0..cdb71ca93 100644
--- a/spec/features/podcasts_spec.rb
+++ b/spec/features/podcasts_spec.rb
@@ -9,8 +9,8 @@
 
     scenario 'Charter should be exist' do
       @podcast = create(:podcast)
-      allow(@podcast).to receive(:exists?) { true }
-      allow(@podcast).to receive(:exists?).with(offset: -1) { false }
+      allow(@podcast).to receive(:exist?) { true }
+      allow(@podcast).to receive(:exist?).with(offset: -1) { false }
       allow(@podcast).to receive(:content) { "title\n収録日: 2019/05/10\n..." }
       allow(Podcast).to  receive(:find_by).with(id: @podcast.id.to_s) { @podcast }
 
@@ -25,7 +25,7 @@
 
     scenario 'Load doc file with absolute path' do
       @podcast = create(:podcast)
-      allow(@podcast).to receive(:exists?) { true }
+      allow(@podcast).to receive(:exist?) { true }
       allow(@podcast).to receive(:content) { "title\n収録日: 2019/05/10\n..." }
       allow(Podcast).to  receive(:find_by).with(id: @podcast.id.to_s) { @podcast }
 
diff --git a/spec/models/podcast_spec.rb b/spec/models/podcast_spec.rb
index ec462a001..353688f31 100644
--- a/spec/models/podcast_spec.rb
+++ b/spec/models/podcast_spec.rb
@@ -10,42 +10,42 @@
     expect(@podcast.path).to eq("public/podcasts/#{@podcast.id}.md")
   end
 
-  describe 'exists?(offset: 0)' do
+  describe 'exist?(offset: 0)' do
     it '\u0000 を含む ⇒ false' do
       allow(@podcast).to receive(:path) { "public/podcasts/\u0000" }
 
-      expect(@podcast.exists?).to eq(false)
+      expect(@podcast.exist?).to eq(false)
     end
 
     context 'offset 省略' do
       before :each do
-        allow(File).to receive(:exists?) { false }
+        allow(File).to receive(:exist?) { false }
       end
 
       it 'ファイルあり ⇒ true' do
-        allow(File).to receive(:exists?).with("public/podcasts/#{@podcast.id}.md") { true }
+        allow(File).to receive(:exist?).with("public/podcasts/#{@podcast.id}.md") { true }
 
-        expect(@podcast.exists?).to eq(true)
+        expect(@podcast.exist?).to eq(true)
       end
 
       it 'ファイルなし ⇒ false' do
-        expect(@podcast.exists?).to eq(false)
+        expect(@podcast.exist?).to eq(false)
       end
     end
 
     context 'offset 指定' do
       before :each do
-        allow(File).to receive(:exists?) { false }
+        allow(File).to receive(:exist?) { false }
       end
 
       it 'ファイルあり ⇒ true' do
-        allow(File).to receive(:exists?).with("public/podcasts/#{@podcast.id + 1}.md") { true }
+        allow(File).to receive(:exist?).with("public/podcasts/#{@podcast.id + 1}.md") { true }
 
-        expect(@podcast.exists?(offset: 1)).to eq(true)
+        expect(@podcast.exist?(offset: 1)).to eq(true)
       end
 
       it 'ファイルなし ⇒ false' do
-        expect(@podcast.exists?(offset: 1)).to eq(false)
+        expect(@podcast.exist?(offset: 1)).to eq(false)
       end
     end
   end
@@ -57,13 +57,13 @@
     end
 
     it 'ファイル存在 ⇒ ファイルから読み込み' do
-      allow(@podcast).to receive(:exists?) { true }
+      allow(@podcast).to receive(:exist?) { true }
 
       expect(@podcast.content).to eq(@content_body)
     end
 
     it 'ファイルなし ⇒ 空文字列' do
-      allow(@podcast).to receive(:exists?) { false }
+      allow(@podcast).to receive(:exist?) { false }
 
       expect(@podcast.content).to eq('')
     end