An access point establishing a wireless LAN is constructed to have a monitor system ‘b’ for monitoring an available channel for communication, in addition to a communication system ‘a’. In the event of detection of radar/radio signals, the access point changes a communication channel used for wireless communication from a current active channel to the monitored channel. Each terminal belonging to the wireless LAN recognizes and follows this channel change by detection of a beacon broadcasted by the access point. In the case of non-detection of radar/radio signals for one minute at the monitored channel, the wireless communication is reestablished immediately at the monitored channel recognized as a CAC (channel availability check)-finished channel. This series of processing is also applicable to inter-access point communication, for example, communication in a WDS (wireless distribution system) mode. This arrangement desirably prevents the potential interruption of wireless communication in a 5 GHz frequency band for a significant period, in the event of detection of radar/radio signals, for example, a weather radar.