The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for reconfiguring a receiver bandwidth by a UE (User Equipment) in the wireless communication system, the method comprising: receiving a message related to SCell activation or deactivation command; determining whether the receiver bandwidth can be reconfigured before a specific time of a HARQ feedback transmission for the message; and reconfiguring the receiver bandwidth before the HARQ feedback transmission for the message if the receiver bandwidth can be reconfigured before the specific time.