diff --git a/README.md b/README.md
index d90ffe023..a0a97eb2f 100644
--- a/README.md
+++ b/README.md
@@ -18,21 +18,13 @@ coming soon
 todo
 
 ## API request
-都度インスタンスやトークンを指定する場合
-``` ts
-import * as Misskey from 'misskey-js';
-
-const meta = await Misskey.api.request('https://misskey.test', 'meta', { detail: true }, 'TOKEN');
-```
-
-最初にインスタンスやトークンを指定し、以後のリクエストでその情報を使いまわす場合
 ``` ts
 import * as Misskey from 'misskey-js';
 
 const cli = new Misskey.api.APIClient({
-	origin: 'https://misskey.test'
+	origin: 'https://misskey.test',
+	credential: 'TOKEN',
 });
-cli.i = { token: 'TOKEN' };
 
 const meta = await cli.request('meta', { detail: true });
 ```
diff --git a/src/api.ts b/src/api.ts
index 3399d57e3..0a106ae91 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -14,54 +14,51 @@ export function isAPIError(reason: any): reason is APIError {
 	return reason[MK_API_ERROR] === true;
 }
 
-export function request<E extends keyof Endpoints>(
-	origin: string,
-	endpoint: E,
-	data: Endpoints[E]['req'] = {},
-	credential: string | null | undefined,
-): Promise<Endpoints[E]['res']> {
-	const promise = new Promise<Endpoints[E]['res']>((resolve, reject) => {
-		// Append a credential
-		if (credential !== undefined) (data as Record<string, any>).i = credential;
-
-		// Send request
-		fetch(`${origin}/api/${endpoint}`, {
-			method: 'POST',
-			body: JSON.stringify(data),
-			credentials: 'omit',
-			cache: 'no-cache'
-		}).then(async (res) => {
-			const body = res.status === 204 ? null : await res.json();
-
-			if (res.status === 200) {
-				resolve(body);
-			} else if (res.status === 204) {
-				resolve(null);
-			} else {
-				reject({
-					[MK_API_ERROR]: true,
-					...body.error
-				});
-			}
-		}).catch(reject);
-	});
-
-	return promise;
-}
-
 export class APIClient {
-	public i: { token: string; } | null = null;
-	private origin: string;
+	public origin: string;
+	public credential: string | null | undefined;
+	public fetch: (typeof fetch);
 
 	constructor(opts: {
 		origin: APIClient['origin'];
+		credential?: APIClient['credential'];
+		fetch?: APIClient['fetch'] | null | undefined;
 	}) {
 		this.origin = opts.origin;
+		this.credential = opts.credential;
+		this.fetch = opts.fetch || fetch;
 	}
 
 	public request<E extends keyof Endpoints>(
 		endpoint: E, data: Endpoints[E]['req'] = {}, credential?: string | null | undefined,
 	): Promise<Endpoints[E]['res']> {
-		return request(this.origin, endpoint, data, credential === undefined ? this.i?.token : credential);
+		const promise = new Promise<Endpoints[E]['res']>((resolve, reject) => {
+			// Append a credential
+			if (this.credential) (data as Record<string, any>).i = this.credential;
+			if (credential) (data as Record<string, any>).i = credential;
+	
+			// Send request
+			this.fetch(`${this.origin}/api/${endpoint}`, {
+				method: 'POST',
+				body: JSON.stringify(data),
+				credentials: 'omit',
+				cache: 'no-cache'
+			}).then(async (res) => {
+				const body = res.status === 204 ? null : await res.json();
+	
+				if (res.status === 200) {
+					resolve(body);
+				} else if (res.status === 204) {
+					resolve(null);
+				} else {
+					reject({
+						[MK_API_ERROR]: true,
+						...body.error
+					});
+				}
+			}).catch(reject);
+		});
+	
+		return promise;
 	}
 }
diff --git a/test/api.ts b/test/api.ts
index fc42c3c26..50a5b641e 100644
--- a/test/api.ts
+++ b/test/api.ts
@@ -1,4 +1,4 @@
-import { request } from '../src/api';
+import { APIClient } from '../src/api';
 import { enableFetchMocks } from 'jest-fetch-mock';
 
 enableFetchMocks();
@@ -21,16 +21,22 @@ describe('API', () => {
 		fetchMock.mockResponse(async (req) => {
 			const body = await req.json();
 			if (req.method == 'POST' && req.url == 'https://misskey.test/api/i') {
-				if (typeof body.i != 'string') {
+				if (body.i === 'TOKEN') {
+					return JSON.stringify({ id: 'foo' });
+				} else {
 					return { status: 400 };
 				}
-				return JSON.stringify({ id: 'foo' });
 			} else {
 				return { status: 404 };
 			}
 		});
 
-		const res = await request('https://misskey.test', 'i', {}, 'TOKEN');
+		const cli = new APIClient({
+			origin: 'https://misskey.test',
+			credential: 'TOKEN',
+		});
+
+		const res = await cli.request('i');
 
 		// validate response
 		expect(res).toEqual({
@@ -60,11 +66,18 @@ describe('API', () => {
 		});
 
 		try {
-			await request('https://misskey.test', 'i', {}, 'TOKEN');
+			const cli = new APIClient({
+				origin: 'https://misskey.test',
+				credential: 'TOKEN',
+			});
+	
+			await cli.request('i');
 		} catch (e) {
 			expect(e.id).toEqual('5d37dbcb-891e-41ca-a3d6-e690c97775ac');
 		}
 	});
 
 	// TODO: ネットワークエラーのテスト
+
+	// TODO: JSON以外が返ってきた場合のハンドリング
 });