diff --git a/src/services/userService.ts b/src/services/userService.ts
new file mode 100644
index 0000000..b1358bb
--- /dev/null
+++ b/src/services/userService.ts
@@ -0,0 +1,17 @@
+import { User } from '@prisma/client';
+import prisma from '@src/prisma';
+
+async function findUserById(userId: string): Promise<User> {
+    return await prisma.user.findUnique({
+        where: {
+            id: userId
+        }
+    }).then(user => {
+        if (!user) {
+            throw new Error('ユーザーが見つかりません');
+        }
+        return user;
+    });
+}
+
+export { findUserById };