The present invention relates to a wireless communication system and, more specifically, to a method and a device for controlling a backoff timer on the basis of multipriority in a wireless communication system. The method for controlling a backoff timer in a terminal in which multipriority is set, according to one embodiment of the present invention, comprises the steps of: transmitting, to a network node, a non access stratum (NAS) request message which is set to a first priority level and does not have an access point name (APN); receiving a reject message for the NAS request message from the network node; and starting a session management (SM) backoff timer on the basis of the rejection message, wherein while the SM backoff timer is operated, the terminal is permitted to transmit a new NAS request message which is not set to the first priority level.