A method for scanning by a STA can comprise the steps of: the STA unicasting a probe request frame to a target AP from a first channel, the target AP having been determined in accordance with a BSSID comprised in a primitive; the STA processing an ACK transmitted via the first channel within a first ACK transmission time, and determining whether the first ACK for the probe request frame is received; if the first ACK is received within the first ACK transmission time, then the STA monitoring a probe response frame, which is a response to the probe request frame from the first channel; and if the first ACK is not received within the first ACK transmission time, then regardless of a CCA level detected during the first ACK transmission time, the STA switching the scanning channel.