An embodiment of the present invention provides a method for accessing to a medium by a station (STA) in a wireless LAN system, the method comprising the steps of: receiving a predetermined frame including a time stamp; identifying a restricted access window (RAW) assignment field included in the predetermined frame; and performing access in a slot determined on the basis of a subfield of the RAW assignment field when the STA belongs to a RAW related to the RAW allocation field, wherein whether the STA belongs to the RAW is determined by whether an association identifier (AID) of the STA is included in a AID range and the RAW assignment field includes a subfield indicating whether the AID range is determined by a TIM bitmap.