diff --git a/src/domain/aggregates/event/Event.ts b/src/domain/aggregates/event/Event.ts
index f0cc4ff..5ee6467 100644
--- a/src/domain/aggregates/event/Event.ts
+++ b/src/domain/aggregates/event/Event.ts
@@ -122,7 +122,7 @@ export class Event {
 
 	public removeMemberId(memberId: string): void {
 		for (const exhibit of this.exhibits) {
-			if (exhibit.getMemberIds().includes(memberId)) {
+			if (exhibit.hasMemberId(memberId)) {
 				throw new ExhibitHasMemberException(exhibit.id, memberId);
 			}
 		}
@@ -135,7 +135,12 @@ export class Event {
 		this.memberIds.add(memberId);
 	}
 
-	public removeExhibitMemberId(exhibitId: string, memberId: string): void {}
+	// NOTE: 展示からの削除のみ行い、Event.memberIdsは操作しない。
+	// 「展示に所属していないがイベント参加者」という状態が有効なため、
+	// イベント参加者からの削除はremoveMemberId()で明示的に行う。
+	public removeExhibitMemberId(exhibitId: string, memberId: string): void {
+		this.getExhibitOrThrow(exhibitId).removeMemberId(memberId);
+	}
 	toSnapshot() {
 		return {
 			id: this.id,
diff --git a/src/domain/aggregates/event/Exhibit.ts b/src/domain/aggregates/event/Exhibit.ts
index b5b965a..d93b057 100644
--- a/src/domain/aggregates/event/Exhibit.ts
+++ b/src/domain/aggregates/event/Exhibit.ts
@@ -95,6 +95,10 @@ export class Exhibit {
 		this.memberIds.delete(memberId);
 	}
 
+	public hasMemberId(memberId: string): boolean {
+		return this.memberIds.has(memberId);
+	}
+
 	private getLightningTalkOrThrow(): LightningTalk {
 		if (!this.lightningTalk) {
 			throw new LightningTalkNotFoundException(
@@ -112,6 +116,7 @@ export class Exhibit {
 			markdownContent: this.markdownContent,
 			url: this.url,
 			lightningTalk: this.lightningTalk?.toSnapshot(),
+			memberIds: Array.from(this.memberIds),
 		};
 	}
 }