To prevent the lowering of driving power-supply voltage in the start of a brushless motor while inhibiting the overshooting of the driving power- supply voltage.

A specified DC power supply is changed into desired DC voltage by chopping-driving a transistor 5a for a DC-to-DC converter 5 in a specified manner, and the DC voltage is used as the power-supply voltage of a motor driver circuit 6. When a pulse signal is input to a control circuit 9 as analog voltage through a filter circuit 8 by a microcomputer 14, the control circuit 9 chopping-drives the transistor 5a and the above-mentioned desired DC voltage is obtained. When the brushless motor 11 is started, the microcomputer 14 uses the output voltage of a starting-voltage compensating circuit 13 as the input analog voltage of the control circuit 9. The starting-voltage circuit 13 outputs voltage corresponding to the output voltage of the DC-to-DC converter 5 to the control circuit 9, and the control circuit 9 chopping-drives the transistor 5a according to the voltage and controls the output voltage of the DC-to-DC converter 5.