The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for handling an ID collision for D2D communication system, the method performed by a first UE comprising: generating a specific ID of the first UE when the first UE is to communicate with a second UE, transmitting a notification message including the specific ID to an eNB, receiving a response message in response to the notification message from the eNB, and generating another ID different from the specific ID if the response message indicates collision of the specific ID.