A master base station according to embodiment divides a bearer of a mobile station into two split bearers in a dual connectivity scheme. One split bearer is provided between the master base station and the mobile station without intervention of a secondary base station. Another split bearer is provided between the master base station and the mobile station with the intervention of a secondary base station. The master base station comprises a transmitter configured to transmit to the mobile station, information indicating whether the mobile station should transmit uplink data to the master station or to the secondary base station.