The present invention relates to a method for a first station (STA) comprising: obtaining available channel information by accessing a database that manages the available channel information within the white space band, and transmitting a white space map (WSM) generated according to the available channel information to a second STA, the WSM includes a channel map field having a variable length, a length field including the length of the channel map field, and map ID information indicating a type of the WSM and whether the WSM being updated; and if the available channel information obtained from the DB indicates that no available channel exists within the white space band, a map ID is set to indicate that the WSM is the updated WSM, and the first STA transmits the WSM which is set as the length field to indicate that the length of the channel map field is 0.