A radio communication system includes a line controller, a plurality of base stations connected to the line controller and a plurality of mobile stations connected to each of the plurality of base stations by radio communication line having control channel and communication channel, and each of the plurality of base stations includes a control unit for monitoring idle slot in the communication channel within a communication area of the base station. The control unit transmits the monitored information of the idle slot to the mobile station within the communication area of the base station at predetermined intervals by using the control channel and each mobile station can use an idle slot in the base station or, if there is no idle slot in the base station, in another base station based on the monitored information of the idle slot to make communication.