A base station (200, 200a) comprising: a radio communication unit configured to establish communication with a mobile communication terminal using a plurality of component carriers; and a control unit configured to: transmit a handover request message to another base station to handover of communication between the mobile communication terminal and the base station (200, 200a) to the another base station; receive a handover request confirm message from the another base station; transmit, after reception of the handover request confirm message, an expansion command to the mobile communication terminal to increase the plurality of component carriers used between the base station (200, 200a) and the mobile communication terminal for increasing the data throughput or increase one or more resource blocks to be allocated to the mobile communication terminal in at least one component carrier from the plurality of component carriers for increasing the data throughput; transmit after transmission of the expansion command or increase of one or more resource blocks, a shrink command to the mobile communication terminal to reduce the plurality of component carriers to one; and transmit after transmission of the shrink command, a handover command for the one component carrier to the mobile communication terminal for handover communication between the mobile communication terminal and the base station (200, 200a) to the another base station. a radio communication unit configured to establish communication with a mobile communication terminal using a plurality of component carriers; and a control unit configured to: transmit a handover request message to another base station to handover of communication between the mobile communication terminal and the base station (200, 200a) to the another base station; receive a handover request confirm message from the another base station; transmit, after reception of the handover request confirm message, an expansion command to the mobile communication terminal to increase the plurality of component carriers used between the base station (200, 200a) and the mobile communication terminal for increasing the data throughput or increase one or more resource blocks to be allocated to the mobile communication terminal in at least one component carrier from the plurality of component carriers for increasing the data throughput; transmit after transmission of the expansion command or increase of one or more resource blocks, a shrink command to the mobile communication terminal to reduce the plurality of component carriers to one; and transmit after transmission of the shrink command, a handover command for the one component carrier to the mobile communication terminal for handover communication between the mobile communication terminal and the base station (200, 200a) to the another base station. transmit a handover request message to another base station to handover of communication between the mobile communication terminal and the base station (200, 200a) to the another base station; receive a handover request confirm message from the another base station; transmit, after reception of the handover request confirm message, an expansion command to the mobile communication terminal to increase the plurality of component carriers used between the base station (200, 200a) and the mobile communication terminal for increasing the data throughput or increase one or more resource blocks to be allocated to the mobile communication terminal in at least one component carrier from the plurality of component carriers for increasing the data throughput; transmit after transmission of the expansion command or increase of one or more resource blocks, a shrink command to the mobile communication terminal to reduce the plurality of component carriers to one; and transmit after transmission of the shrink command, a handover command for the one component carrier to the mobile communication terminal for handover communication between the mobile communication terminal and the base station (200, 200a) to the another base station.