The present invention relates to a wireless communication system and, more specifically, provides a method and device for transmitting/receiving a frame in accordance with the bandwidth thereof in a WLAN system. The method whereby a station (STA) performs virtual carrier sensing (VCS) in a WLAN system according to one embodiment of the present invention may comprise the steps of: receiving a frame by the STA; determining by the STA, a VCS time length value on the basis of the response indication parameter and/or channel bandwidth type of the frame; and deferring channel access by the STA for the VCS time length value.