A series regulator for outputting a regulated voltage and a booster circuit of a charge pump type for outputting an output voltage by boosting the regulated voltage are connected in series. The series regulator is controlled so that the output voltage is maintained constant. A main circuit current of the series regulator is subject to current limitation. An excess signal commensurate of an excess of a current indicator value over a current reference value is generated. A voltage control signal is reduced in level in accordance with the excess signal.