The present document relates to a wireless communication system and, more particularly, to a method for establishing a wireless channel by an AP in a high-density wireless LAN system and to an apparatus therefor. The AP configured for this purpose can establish a primary channel and one or more secondary channels, establish one or more downlink oriented channels into one or more secondary channels, but without the one or more downlink oriented channels overlapping the primary channel of an adjacent basic service set (BSS), and transmit, to a station connected to the AP, the frame including establishment information on the established one or more downlink oriented channels.