A radio base station includes a mobile communication system, a relay node and a radio base station connected via a radio bearer. A mobile station is configured to perform a handover process between a state in which a radio bearer is set with the relay node so as to communicate via the relay node and the radio base station, and a state in which a radio bearer is set with the radio base station so as to communicate via the radio base station. The handover process is configured such that a data signal is transferred via the radio bearer between the relay node and the radio base station.