diff --git a/packages/backend/src/services/logger.ts b/packages/backend/src/services/logger.ts
index bdae3f876..388e2e87e 100644
--- a/packages/backend/src/services/logger.ts
+++ b/packages/backend/src/services/logger.ts
@@ -6,9 +6,10 @@ import * as SyslogPro from 'syslog-pro';
 import config from '@/config/index.js';
 import { envOption } from '@/env.js';
 
+type KeywordColor = Parameters<typeof convertColor.keyword.rgb>[0];
 type Domain = {
 	name: string;
-	color?: string;
+	color?: KeywordColor;
 };
 
 type Level = 'error' | 'success' | 'warning' | 'debug' | 'info';
@@ -17,9 +18,9 @@ export default class Logger {
 	private domain: Domain;
 	private parentLogger: Logger | null = null;
 	private store: boolean;
-	private syslogClient: any | null = null;
+	private syslogClient: SyslogPro.RFC5424 | null = null;
 
-	constructor(domain: string, color?: string, store = true) {
+	constructor(domain: string, color?: KeywordColor, store = true) {
 		this.domain = {
 			name: domain,
 			color,
@@ -41,7 +42,7 @@ export default class Logger {
 		}
 	}
 
-	public createSubLogger(domain: string, color?: string, store = true): Logger {
+	public createSubLogger(domain: string, color?: KeywordColor, store = true): Logger {
 		const logger = new Logger(domain, color, store);
 		logger.parentLogger = this;
 		return logger;
@@ -57,7 +58,7 @@ export default class Logger {
 		}
 
 		const time = dateFormat(new Date(), 'HH:mm:ss');
-		const worker = cluster.isPrimary ? '*' : cluster.worker.id;
+		const worker = cluster.isPrimary ? '*' : cluster.worker!.id;
 		const l =
 			level === 'error' ? important ? chalk.bgRed.white('ERR ') : chalk.red('ERR ') :
 			level === 'warning' ? chalk.yellow('WARN') :
@@ -85,7 +86,6 @@ export default class Logger {
 					level === 'error' ? this.syslogClient.error :
 					level === 'warning' ? this.syslogClient.warning :
 					level === 'success' ? this.syslogClient.info :
-					level === 'debug' ? this.syslogClient.info :
 					level === 'info' ? this.syslogClient.info :
 					null as never;
 
@@ -94,7 +94,7 @@ export default class Logger {
 		}
 	}
 
-	public error(x: string | Error, data?: Record<string, any> = {}, important = false): void { // 実行を継続できない状況で使う
+	public error(x: string | Error, data: Record<string, any> = {}, important = false): void { // 実行を継続できない状況で使う
 		if (x instanceof Error) {
 			data.e = x;
 			this.log('error', x.toString(), data, important);