A secondary base station according to an embodiment is configured to connect to a master base station via an X2 interface and for being used for a dual connectivity communication, which is to transmit downlink data from the master base station through a split bearer to a user equipment. The secondary base station comprises: a receiver configured to receive the downlink data transferred from the master base station; a transmitter configured to transmit the downlink data received by the receiver to the user equipment; and a controller configured to determine a release of the split bearer. The transmitter configured to transmit a release request message for requesting the release of the split bearer to the master base station in response to determining the release of the split bearer.