PURPOSE: To suppress the overheat and the noise of a motor by accelerating operating speed by driving the motor by the almost full voltage when acceleration and deceleration are performed and decreasing a voltage in an ordinary sewing operation by inputting a frequency command and a voltage command to an inverter part via a delay circuit.

CONSTITUTION: The output of a frequency delay circuit 21 is inputted to the frequency command input 16 of the inverter part 15, and that of a voltage delay circuit 22 to the voltage command input 17. For example, the inverter part 15 drives the motor 14 by the voltage of nearly 100% for a steep operation with rise time less than 50ms, and accelerates the motor according to the rise time 200ms of the frequency command. Meanwhile, the inverter part 15 drives the motor 14 by a low voltage for a moderate operation with rise time exceeding 200ms when a frequency is low. Thereby, it is possible to accelerate the operating speed by driving the motor 14 by the almost full voltage in acceleration/deceleration, and to suppress the heat and the noise of the motor 14 by decreasing the voltage when the ordinary sewing operation is performed.