A radio device, which is the source, transmits a route request packet (RREQ) to a radio device. In response to the route request packet (RREQ), the radio device transmits to the radio device a route setup packet (RSET) including a route Radio Device Radio Device Radio Device Radio Device by looking-up topology information (TPIF). In response to the route setup packet (RSET), the radio device produces a route notification packet (RNTF) and transmits the produced route notification packet (RNTF) to radio devices, and. In response to the route notification packet (RNTF), the radio device, which is the destination, produces a route reply packet (RREP) and transmits the produced route reply packet (RREP) to the radio device, which is the source.