PURPOSE: To obtain a driving device of a polisher being so designed as to prevent an overcurrent from flowing through an electric light line of an input in any loaded state, by combining a variable-frequency inverter with a three- phase induction motor.

CONSTITUTION: The number of revolutions of a motor 18 is detected by a revolutions detector 19 and a signal 20 thereof is inputted to an arithmetic unit 14. Meanwhile, a signal 13 set by a revolutions setting unit 12 is also inputted to the arithmetic unit 14. In the arithmetic unit 14, a voltage and a frequency are computed so that a torque be the maximum in a prescribed input current of the motor, by using the set number of revolutions and an intrinsic set number of revolutions of the motor, and they are inputted to a variable- frequency inverter 17. Thereby the motor is driven by a minimum current at any number of revolutions and thus a driving device of a polisher which can prevent an overcurrent from flowing through an electric light line of an input.