It is judged whether a mobile node 11 exists at a boundary A overlapped with a different sector of the base station for use in communication or at a boundary B overlapped with an area of another base station or at an area fringe C. In accordance with the application in use and the results thus judged, a handover is performed between base stations in a wireless communication system, or switching to the another wireless communication system is made, or simultaneous communication with the another wireless communication system is performed, or either the uplink or the downlink is switched to the another wireless communication system.