The present invention eliminates a transmission-waiting operation which is unnecessary while accommodating a prioritized traffic. Although a communication station enters a transmission-disallowed state in response to detection of a signal addressed to another station in accordance with medium access control based on CSMA, if the communication station receives a frame transmitted with priority to a local station during the transmission waiting, it cancels the transmission-disallowed state, sends back a frame responding the frame transmitted with priority and effectively operates a transmission prioritized period. The communication station starts a search procedure to perform a processing of evading duplication of the transmission prioritized periods if it judges a possibility of a problem occurring in a time zone in which reception with priority is possible.