A disclosed base station gateway apparatus has a C-plane processing unit and a U-plane processing unit. When a mobile station performs handover from a subordinate source base station to a subordinate target base station, the C-plane processing unit terminates S1AP signaling received from the source base station and the target base station without relaying the S1AP signaling to a mobility management apparatus. The U-plane processing unit inserts, into U-plane data that is received from a serving gateway apparatus and that is to be transferred to the source base station, an end marker indicating that the U-plane data is the last data at a predetermined timing, and switches the transfer destination of the U-plane data, received from the serving gateway apparatus, from the source base station to the target base station at a timing immediately after the end marker is inserted.