diff --git a/.github/actions/setup-build-env/action.yml b/.github/actions/setup-build-env/action.yml
new file mode 100644
index 0000000..2da3120
--- /dev/null
+++ b/.github/actions/setup-build-env/action.yml
@@ -0,0 +1,18 @@
+name: Setup build environment
+description: Android のビルドに必要な JDK・Android SDK・Gradle を用意する。
+
+runs:
+  using: composite
+  steps:
+    - uses: actions/setup-java@v6
+      with:
+        distribution: temurin
+        java-version: '25.0.4+101.0.LTS'
+
+    - uses: android-actions/setup-android@v4
+      with:
+        # 既定値に含まれる旧 `tools` は SDK リポジトリから削除済みで sdkmanager が失敗するため、
+        # 必要なパッケージだけを明示する。
+        packages: platform-tools
+
+    - uses: gradle/actions/setup-gradle@v6
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index f2c923f..01fc562 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -17,14 +17,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - uses: actions/setup-java@v6
-        with:
-          distribution: temurin
-          java-version: '17'
-
-      - uses: android-actions/setup-android@v4
-
-      - uses: gradle/actions/setup-gradle@v6
+      - uses: ./.github/actions/setup-build-env
 
       # 署名鍵が登録されていればリリース署名を行う。未登録なら未署名APKになる。
       - name: Decode keystore
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2880db6..81e6c09 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -16,14 +16,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - uses: actions/setup-java@v6
-        with:
-          distribution: temurin
-          java-version: '17'
-
-      - uses: android-actions/setup-android@v4
-
-      - uses: gradle/actions/setup-gradle@v6
+      - uses: ./.github/actions/setup-build-env
 
       # ユニットテストに加え、リソースやマニフェストの不整合を拾うためビルドと lint も通す。
       - name: Test and build
@@ -35,14 +28,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - uses: actions/setup-java@v6
-        with:
-          distribution: temurin
-          java-version: '17'
-
-      - uses: android-actions/setup-android@v4
-
-      - uses: gradle/actions/setup-gradle@v6
+      - uses: ./.github/actions/setup-build-env
 
       # エミュレータのハードウェアアクセラレーションを有効にする。
       - name: Enable KVM
diff --git a/app/build.gradle b/app/build.gradle
index 09370f8..a4d2a2b 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -40,8 +40,8 @@ android {
     }
 
     compileOptions {
-        sourceCompatibility = JavaVersion.VERSION_17
-        targetCompatibility = JavaVersion.VERSION_17
+        sourceCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_21
     }
 }