diff --git a/src/msw/handlers/Viewer.ts b/src/msw/handlers/Viewer.ts
new file mode 100644
index 0000000..40fe31a
--- /dev/null
+++ b/src/msw/handlers/Viewer.ts
@@ -0,0 +1,29 @@
+import { graphql } from "msw";
+
+import { mockAvatars } from "~/mocks/assets";
+import { FetchViewerDocument } from "~/mocks/codegen";
+
+export const queryFetchViewer = graphql.query(
+  FetchViewerDocument,
+  (req, res, ctx) => {
+    if (!req.headers.get("Authorization")) {
+      return res(ctx.data({ __typename: "Query", viewer: null }));
+    }
+
+    // eslint-disable-next-line no-process-env
+    if (process.env.NEXT_PUBLIC_MSW_FIRST_NEED_REGISTER === "true") {
+      return res(ctx.data({ __typename: "Query", viewer: null }));
+    }
+
+    return res(ctx.data({
+      __typename: "Query",
+      viewer: {
+        __typename: "User",
+        id: "viewer",
+        alias: "viewer",
+        displayName: "Viewer",
+        avatar: mockAvatars.viewer,
+      },
+    }));
+  },
+);
diff --git a/src/msw/handlers/index.ts b/src/msw/handlers/index.ts
index 560a0b4..46de988 100644
--- a/src/msw/handlers/index.ts
+++ b/src/msw/handlers/index.ts
@@ -7,8 +7,12 @@ import { queryGlobalNavNotifications } from "./GlobalNav";
 import { queryAllHenkenPages, queryHenkenPage } from "./HenkenPage";
 import { mutationRegisterUser, queryIsAliasUnique } from "./RegisterUserForm";
 import { queryAllUserPages, querySendHenkensUserPage, queryUserPage } from "./UserPage";
+import { queryFetchViewer } from "./Viewer";
 
 export const handlers = [
+  // Viewer
+  queryFetchViewer,
+
   // Henken Page
   queryAllHenkenPages,
   queryHenkenPage,