diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index e80eabb..7671f58 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -21,7 +21,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@319994f95fa847cf3fb3cd3dbe89f6dcde9f178f # v1
       with:
-        ruby-version: '3.0'
+        ruby-version: '4.0.3'
         bundler-cache: true
 
     - name: Setup Node.js
diff --git a/.ruby-version b/.ruby-version
index f989260..c4e41f9 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.4.4
+4.0.3
diff --git a/Dockerfile b/Dockerfile
index bdcac0b..d0d0322 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:3.4-slim
+FROM ruby:4.0-slim
 
 # 基本的なツールのインストール
 RUN apt-get update && apt-get install -y \