A radio base station according to the present invention comprising : a mobile communication system, a first relay node and a radio base station are connected via a radio bearer, a second relay node and a radio base station are connected via a radio bearer, a mobile station is configured so as to conduct a handover process between a first state wherein a radio bearer is established with the first relay node in order to communicate via the first relay node and the radio base station, and a second state wherein a radio bearer is established with the second relay node in order to communicate via the second relay node and the radio base station and the mobile station is configured such that in the handover process, control signals involved in the handover process are transmitted and received via the radio bearer between the first relay node and the radio base station, and via the radio bearer between the second relay node and the radio base station.