Abstract: Disclosed is a mobile communication device which has: a position registration controller which controls a position registration process where a position of the mobile communication device is registered to a base station; a transmitting circuit which transmits a position registration control signal for the mobile communication device which is processed by the position registration controller; a receiving circuit which receives a position registration control signal for the base station to be transmitted from the base station; a high-speed movement judging circuit which judges whether the mobile communication device is moving at a high speed or not by monitoring an interval of position registration; a power source controller which controls a power source to be supplied to functional circuits with an intermittent operation time to be determined by an output of the high-speed movement judging circuit; a power circuit which supplies the power source to the functional circuits except at least the power source contr