The present document relates to a backoff procedure and apparatus for efficiently accessing a broadband channel in a wireless LAN system. To this end, a station performs a clear channel assessment (CCA) operation in each of a plurality of channels, and when one or more of the plurality of channels is/are not used and the one or more channels is/are not used for frame transmission in the basic service set (BSS) of its/their station, the station is characterized in that it performs or re-performs a backoff procedure in the one or more channels. When a backoff counter value becomes zero according to the backoff procedure, the station may transmit a frame through the one or more channels.