For continuous data transmission during a handover procedure, Make-Before-Break handover may be introduced, which maintains source evolved NodeB (eNB) connection after reception of radio resource control (RRC) message for handover. In order to reduce ambiguity of Make-Before-Break handover, the present invention provides receiving a handover command from a network, after receiving the handover command from the network, keeping exchanging data with a source cell, stopping exchanging data with the source cell when a condition is met, and after stopping exchanging data with the source cell, starting exchanging data with a target cell.