A handover control system in a mobile communication system includes; a first handover processing unit for controlling forwarding of user data from a source radio base station to a target radio base station in handover processing caused by movement of a mobile communication terminal; a second handover processing unit for controlling transmission of the user data from an upper layer node to both the source radio base station and the target radio base station in the handover processing; and a control unit for selecting activating either the first handover processing means or the second handover processing means according to a preliminarily requested communication quality for the user data.