An access point includes: detection means detecting radar signal; detection notification means notifying other access point of radar signal detection; assessment means assessing whether to own authority to determine channel used among access points; determination means determining channel used among access points when detection means detects radar signal or when other access point notifies of radar signal detection, when owning authority; channel notification means notifying other access point of the channel determined by determination means; and change means changing the channel used between other access point to either the channel determined by determination means or to a channel notified from other access point. When a plurality of access points detect radar signal, entire system is operable through new channel.