diff --git a/src/main/java/cactusServer/models/CollisionManager.java b/src/main/java/cactusServer/models/CollisionManager.java
index 3ffe8f1..8f089d1 100644
--- a/src/main/java/cactusServer/models/CollisionManager.java
+++ b/src/main/java/cactusServer/models/CollisionManager.java
@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.Map;
 
 import org.ntlab.radishforandroidstudio.framework.model3D.CollisionResult;
@@ -44,7 +45,7 @@
 			Instance instance = Instances.getInstance().getInstance(instanceId);
 			instance.getUniverse().update(interval);
 			collisionPlayersObjects(instanceId, instance);
-			collisionBulletsAndOthers(instanceId, instance);
+//			collisionBulletsAndOthers(instanceId, instance);
 		}
 	}
 
@@ -92,35 +93,69 @@
 		object.setPosition(new Position3D(vec));
 	}
 	
+//	private void collisionBulletsAndOthers(String instanceId, Instance instance) {
+//		System.out.println("a");
+//		for (Map.Entry<String, HashMap<String, Bullet>> playersBulletsEntry : instance.getBullets().entrySet()) {
+//			String bulletOwnerPlayerId = playersBulletsEntry.getKey();
+//			Map<String, Bullet> bulletMap = playersBulletsEntry.getValue();
+//			for (Map.Entry<String, Bullet> bulletEntry : bulletMap.entrySet()) {
+//				String bulletId = bulletEntry.getKey();
+//				Bullet bullet = bulletEntry.getValue();
+//				System.out.println("b");
+//				collisionBulletAndPlayers(instanceId, instance, bulletOwnerPlayerId, bulletId, bullet);
+//				System.out.println("c");
+//				collisionBulletAndObjects(instance, bulletOwnerPlayerId, bulletId, bullet);
+//				System.out.println("d");
+//			}
+//		}
+//	}
+	
 	private void collisionBulletsAndOthers(String instanceId, Instance instance) {
-		for (Map.Entry<String, HashMap<String, Bullet>> playersBulletsEntry : instance.getBullets().entrySet()) {
+		System.out.println("a");
+//		for (Map.Entry<String, HashMap<String, Bullet>> playersBulletsEntry : instance.getBullets().entrySet()) {
+		Iterator<Map.Entry<String, HashMap<String, Bullet>>> playersBulletsEntryIt = instance.getBullets().entrySet().iterator();
+		while (playersBulletsEntryIt.hasNext()) {
+			Map.Entry<String, HashMap<String, Bullet>> playersBulletsEntry = playersBulletsEntryIt.next();
 			String bulletOwnerPlayerId = playersBulletsEntry.getKey();
 			Map<String, Bullet> bulletMap = playersBulletsEntry.getValue();
-			for (Map.Entry<String, Bullet> bulletEntry : bulletMap.entrySet()) {
+//			for (Map.Entry<String, Bullet> bulletEntry : bulletMap.entrySet()) {
+			Iterator<Map.Entry<String, Bullet>> bulletEntryIt = bulletMap.entrySet().iterator();
+			while (bulletEntryIt.hasNext()) {
+				Map.Entry<String, Bullet> bulletEntry = bulletEntryIt.next();
 				String bulletId = bulletEntry.getKey();
 				Bullet bullet = bulletEntry.getValue();
-				collisionBulletAndPlayers(instanceId, instance, bulletOwnerPlayerId, bulletId, bullet);
-				collisionBulletAndObjects(instance, bulletOwnerPlayerId, bulletId, bullet);
+				System.out.println("b");
+				collisionBulletAndPlayers(instanceId, instance, bulletOwnerPlayerId, bulletId, bullet, bulletEntryIt);
+				System.out.println("c");
+				collisionBulletAndObjects(instance, bulletOwnerPlayerId, bulletId, bullet, bulletEntryIt);
+				System.out.println("d");
 			}
 		}
 	}
 	
-	private void collisionBulletAndPlayers(String instanceId, Instance instance, String bulletOwnerPlayerId, String bulletId, Bullet bullet) {
+	private void collisionBulletAndPlayers(String instanceId, Instance instance, String bulletOwnerPlayerId, String bulletId, Bullet bullet, Iterator<Map.Entry<String, Bullet>> bulletEntryIt) {
 		Instances instances = Instances.getInstance();
 		for (Map.Entry<String, Player> playersEntry : instances.getPlayers(instanceId).entrySet()) {
 			if (isCollision(bullet, playersEntry.getValue())) {
 				if (!(playersEntry.getKey().equals(bulletOwnerPlayerId))) {
 					// Player(����������)�ƒe�������������̏���������
 				}
-				instance.destroyBullet(bulletOwnerPlayerId, bulletId); // Player(�������܂�)�ɓ��������e������
+//				instance.destroyBullet(bulletOwnerPlayerId, bulletId); // Player(�������܂�)�ɓ��������e������
+				bulletEntryIt.remove();
+				instance.getUniverse().displace(bullet.getPlaceable());
 			}
 		}
 	}
 	
-	private void collisionBulletAndObjects(Instance instance, String bulletOwnerPlayerId, String bulletId, Bullet bullet) {
+	private void collisionBulletAndObjects(Instance instance, String bulletOwnerPlayerId, String bulletId, Bullet bullet, Iterator<Map.Entry<String, Bullet>> bulletEntryIt) {
+		System.out.println("c1");
 		for (Object object : instance.getObjects().values()) {
 			if (isCollision(bullet, object)) {
-				instance.destroyBullet(bulletOwnerPlayerId, bulletId);
+				System.out.println("c2");
+//				instance.destroyBullet(bulletOwnerPlayerId, bulletId);
+				bulletEntryIt.remove();
+				instance.getUniverse().displace(bullet.getPlaceable());
+				System.out.println("c3");
 			}
 		}
 	}