A radio communication system comprising: a first base station configured to operate a first cell; a second base station configured to operate a second cell; a core network comprising a mobility management apparatus and a data transfer apparatus; and a mobile station, wherein the first base station is configured to establish a first signaling bearer with the mobility management apparatus, establish a second signaling bearer with the second base station, and establish a signaling radio bearer with the mobile station in the first cell, the second base station is configured to establish the second signaling bearer with the first base station, establish a data bearer with the data transfer apparatus, and establish a data radio bearer with the mobile station in the second cell, the first base station is further configured to send, to the second base station via the second signaling bearer, first configuration information that is necessary to establish the data bearer and the data radio bearer in the second base station, and the first base station is further configured to keep the first configuration information in the first base station even after the data bearer and the data radio bearer are established in the second base station, the first configuration information comprises at least one of an identifier of the data bearer, QoS information of the data bearer, an address of the data transfer apparatus, and a tunnel endpoint identifier of the data transfer apparatus, the first base station is configured to, when an endpoint of the data radio bearer and an endpoint of the data bearer are changed from the second base station to a third base station, send the first configuration information, which has been kept in the first base station, to the third base station, and the first base station is configured to, when the endpoint of the data radio bearer and the endpoint of the data bearer are changed from the second base station to the third base station, generate, based on the first configuration information, third configuration information to establish the data radio bearer between the mobile station and the third base station and transmit the third configuration information to the mobile station via the signaling radio bearer. a first base station configured to operate a first cell; a second base station configured to operate a second cell; a core network comprising a mobility management apparatus and a data transfer apparatus; and a mobile station, wherein the first base station is configured to establish a first signaling bearer with the mobility management apparatus, establish a second signaling bearer with the second base station, and establish a signaling radio bearer with the mobile station in the first cell, the second base station is configured to establish the second signaling bearer with the first base station, establish a data bearer with the data transfer apparatus, and establish a data radio bearer with the mobile station in the second cell, the first base station is further configured to send, to the second base station via the second signaling bearer, first configuration information that is necessary to establish the data bearer and the data radio bearer in the second base station, and the first base station is further configured to keep the first configuration information in the first base station even after the data bearer and the data radio bearer are established in the second base station, the first configuration information comprises at least one of an identifier of the data bearer, QoS information of the data bearer, an address of the data transfer apparatus, and a tunnel endpoint identifier of the data transfer apparatus, the first base station is configured to, when an endpoint of the data radio bearer and an endpoint of the data bearer are changed from the second base station to a third base station, send the first configuration information, which has been kept in the first base station, to the third base station, and the first base station is configured to, when the endpoint of the data radio bearer and the endpoint of the data bearer are changed from the second base station to the third base station, generate, based on the first configuration information, third configuration information to establish the data radio bearer between the mobile station and the third base station and transmit the third configuration information to the mobile station via the signaling radio bearer.