A mobile communication system uses efficiently a radio band of a previously-connected base station, when a mobile terminal that executes multicast communication moves among radio base stations. The mobile communication system includes a layer-2 switch. Upon switching from one radio base station over to the other radio base station, the mobile terminal transmits a path formation request related to a multicast group via the connected radio base station. The path formation request reaches the wired port of the one radio base station through the layer-2 switch. Here, “leave” of the mobile terminal from the control of the one radio base station is detected, and the delivery of multicast is halted. The other radio base station, on the other hand, starts delivering the multicast.