1. A method of performing random access to an access point (AP) by a station (STA) operating in a wireless local area network (WLAN) system, the method comprising:receiving a first frame including resource allocation information for a random access from the AP;
performing backoff using a backoff count based on a predetermined contention window size in resources allocated based on the resource allocation information for the random access;
performing clear channel assessment (CCA) by the STA for the resources allocated based on the resource allocation information for the random access to adjust transmission of a second frame through a randomly selected resource based on a result of CCA,
wherein the second frame is not transmitted at a first timing at which the backoff count reaches 0, when the randomly selected resource at the first timing is busy as the result of CCA;
receiving a third frame including second resource allocation information for a subsequent random access from the AP; and
transmitting the second frame at a second timing through a second randomly selected resource from among resources allocated based on the second resource allocation information of the third frame,
wherein when the third frame is received, the second timing is determined while the backoff count is maintained at 0.