Radio base stations connect by radio lines with radio terminals in cells that make up each radio base station and relay data communication realized by the radio terminals on bearers on radio lines. Base station controllers record correspondence information of the data flow of data communication with the radio terminals and the bearers on the radio lines and, by referring to the correspondence information, effects termination of data communication with the radio terminals. When, in a state in which a drift base station controller relays and transfers data communication between radio base stations to which the radio terminals are connected and a serving base station controller, the serving base station controller is transferred to the drift base station controller, the plurality of base station controllers then report to the drift base station controller the correspondence information from the serving base station controller.