diff --git a/apps/api/src/services/google/gemini-api.ts b/apps/api/src/services/google/gemini-api.ts
index b10e5bf..a40d420 100644
--- a/apps/api/src/services/google/gemini-api.ts
+++ b/apps/api/src/services/google/gemini-api.ts
@@ -6,7 +6,7 @@ import type { Difficulty } from '../../types';
 
 const API_ENDPOINT_BASE =
   'https://generativelanguage.googleapis.com/v1beta/models';
-const MODEL_NAME = 'gemini-2.5-flash';
+const MODEL_NAME = 'gemini-1.5-flash';
 
 /**
  * Gemini API に投げるプロンプト