Gateway and control device, and communication controlling methods for the same

In order to implement handover to a femto cell without making any modification to UEs, a gateway (50) relays traffic between a core network (60, 70) and a plurality of base stations (20_1-20_4) that are respectively incorporated into the core network (60, 70) through a public network. The gateway (50) generates an RRC Connection Release message for prompting establishment of a new RRC connection, when it is notified from the core network (60, 70) that a mobile station (10) is handed over to any one of the plurality of base stations (20_1-20_4). Then, the gateway (50) causes the core network (60, 70) to instruct a control device (40), which has established an RRC connection to the mobile station (10), to transfer the RRC Connection Release message to the mobile station (10).