diff --git a/packages/backend/src/queue/processors/InboxProcessorService.ts b/packages/backend/src/queue/processors/InboxProcessorService.ts
index 931d4a412f..8bc981e10a 100644
--- a/packages/backend/src/queue/processors/InboxProcessorService.ts
+++ b/packages/backend/src/queue/processors/InboxProcessorService.ts
@@ -234,6 +234,7 @@ export class InboxProcessorService implements OnApplicationShutdown {
 
 		// アクティビティを処理
 		try {
+			this.logger.debug('performing activity', { activityId: activity.id, actorUri: authUser.user.uri, actorId: authUser.user.id, activity });
 			const result = await this.apInboxService.performActivity(authUser.user, activity);
 			if (result && !result.startsWith('ok')) {
 				this.logger.warn(`inbox activity ignored (maybe): id=${activity.id} reason=${result}`);
diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index 5cf9a0a5ed..f8b598a92b 100644
--- a/packages/backend/src/server/ActivityPubServerService.ts
+++ b/packages/backend/src/server/ActivityPubServerService.ts
@@ -115,6 +115,7 @@ export class ActivityPubServerService {
 	@bindThis
 	private async inbox(request: FastifyRequest, reply: FastifyReply) {
 		if (this.meta.federation === 'none') {
+			this.inboxLogger.debug('federation is disabled');
 			reply.code(403);
 			return;
 		}
@@ -148,17 +149,18 @@ export class ActivityPubServerService {
 					delay: 300_000,
 				},
 			});
-		} catch (err) {
-			this.inboxLogger.warn('signature header parsing failed', { err });
 
+			this.inboxLogger.debug('signature header parsed', { signature, body: request.body });
+		} catch (err) {
 			if (typeof request.body === 'object' && 'signature' in request.body) {
 				// LD SignatureがあればOK
 				this.queueService.inbox(request.body as IActivity, null);
+				this.inboxLogger.debug('LD Signature found in request body', { err, body: request.body });
 				reply.code(202);
 				return;
 			}
 
-			this.inboxLogger.warn('signature header parsing failed and LD signature not found');
+			this.inboxLogger.warn('signature header parsing failed and LD signature not found', { err });
 			reply.code(401);
 			return;
 		}