A radio base station includes a mobile communication system, a first relay node and a first radio base station connected via a radio bearer, a second relay node, and a second radio base station connected via a radio bearer. The first radio base station and the second radio base station are connected via a bearer, in which a mobile station is configured so as to conduct a handover process between a first and second state. In the first state a radio bearer is established with the first relay node in order to communicate. In the second state a radio bearer is established with the second relay node in order to communicate. The mobile station is configured such that in the handover process, control signals are transmitted and received via the radio bearer between the first relay node, first radio base station, second radio base station, and second relay node.