PURPOSE: To keep the number of revolutions of a motor constant against the fluctuation in a supply voltage over a wide range by correcting the difference in current characteristics generated between a reference transistor and current regulation transistor, as the supply voltage changes, through providing a correction resistor and through causing a compensation current to flow.

CONSTITUTION: When the number of revolutions of a motor M lowers due to a load becoming heavier, etc., a counter electromotive force lowers, the potential of the connection of voltage divider resistors RA and RB rises and an error amplifier OP operates so that the current quantity of a reference transistor QA and current regulation transistor QB becomes higher and the number of revolutions of the motor M is maintained at a constant value. For the purpose of compensating the difference in characteristics of the reference transistor QA and current regulation transistor QB accompanying the fluctuation in a supply voltage VCC, in this case, a correction resistor RV with high value of resistance is connected between the connection of resistors RT and RA and earth and a current proportional to the potential of the connection of the resistors RT and RA is caused to flow so that a motor M is rotated at a constant speed also against the fluctuation in the supply voltage.