diff --git a/src/main/java/cactusServer/models/Instances.java b/src/main/java/cactusServer/models/Instances.java
index 0180e76..04dbad1 100644
--- a/src/main/java/cactusServer/models/Instances.java
+++ b/src/main/java/cactusServer/models/Instances.java
@@ -1,6 +1,8 @@
 package cactusServer.models;
 
 import java.util.HashMap;
+import java.util.HashSet;
+
 import cactusServer.entities.Instance;
 
 /**
@@ -11,7 +13,8 @@
  */
 public class Instances {
 	private static Instances theInstance = null;
-	private HashMap<String, Instance> instanceMap = new HashMap<>();
+	private HashMap<String, Instance> instanceMap = new HashMap<>(); // instance��ID�Ǝ��̂��Ǘ�
+	private HashSet<String> instanceIdSet = new HashSet<>(); // �g�p�ς�ID�̏W��
 
 	private Instances() {
 
@@ -36,9 +39,13 @@
 	 *            Instance�����ʂ����ӂ�ID
 	 * @param name
 	 *            �C���X�^���X�� (��)
-	 * @return �V�����쐬���ꂽInstance
+	 * @return �V�����쐬���ꂽInstance<br>
+	 *         ������, instanceID���d�������ꍇ�͐V�KInstance���쐬������null��Ԃ�
 	 */
 	public Instance createInstance(String instanceId, String name) {
+		if (!instanceIdSet.add(instanceId)) {
+			return null;
+		}
 		Instance instance = new Instance(name);
 		instanceMap.put(instanceId, instance);
 		return instance;
@@ -55,4 +62,15 @@
 		return instanceMap.get(instanceId);
 	}
 
+	/**
+	 * ID�ɑΉ�����Instance��Map����폜���ĕԂ�
+	 * 
+	 * @param instanceId
+	 *            Instance�����ʂ����ӂ�ID
+	 * @return Map����폜���ꂽInstance
+	 */
+	public Instance destroyInstance(String instanceId) {
+		return instanceMap.remove(instanceId);
+	}
+
 }