To solve the problem wherein a terminal cannot perform data communication from a network from the time point of a terminal receiving a handover command (HO command) message from a base station controlling a source cell to the time point of a terminal receiving a handover complete (HO complete) message from a base station controlling a target cell, after the terminal transmits the handover command message to the base station controlling the source cell, the base station controlling the source cell transmits to the base station controlling the target cell whether or not the terminal supports a function of reducing the interruption time of data transfer, the terminal continues to perform data transmission/reception with the base station controlling the source cell, and after the terminal completes a random access procedure with the base station controlling the target cell, the base station controlling the source cell transmits an additional sequence number status transfer message to the base station controlling the target cell.