A first access network in which a bearer transfer path that guarantees a predetermined QoS has been established and a second access network in which a transfer path which is different from that in the first access network has been established are provided, and PCRF 60 transmits to a mobile station an uplink traffic switching request including information of a flow of which the access system type is switched, out of flows in which a UE 10 performs communication, and information of an access system type to be a switching destination of the flow, and the UE 10, upon receiving the uplink traffic switching request, switches a transfer path of the flow included in the uplink traffic switching request to that of the access system type. This makes it possible to provide a mobile communication system or the like in which a transmission path of a flow established by a mobile station capable of being simultaneously connected to a plurality of radio access networks is able to be switched without making alterations to all the radio access networks, with initiative taken by a control station installed in a core network.