diff --git a/README.md b/README.md
index 146f407..4053112 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@ The app will exit on the first touch event.
 Dependencies
 ------------
 
+The minimum required version of Android is 4.0.3 (Ice Cream Sandwich MR1).
+
 This project depends on the Allegro game development library (http://liballeg.org);
 the dependency is automatically resolved by Android Studio using the Maven AAR
 distribution of Allegro (https://bintray.com/liballeg/maven).
diff --git a/app/build.gradle b/app/build.gradle
index 3bd451f..6f6a976 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -4,7 +4,7 @@ android {
     compileSdkVersion 27
     defaultConfig {
         applicationId "com.tksls.yellowrectangle"
-        minSdkVersion 23
+        minSdkVersion 15
         targetSdkVersion 27
         versionCode 1
         versionName "1.0"