PURPOSE: To improve the resolution of output voltage, by arranging a PWM pattern memory provided with a plurality of data table sets, a data table selecting means, and a PWM data reading-out means.

CONSTITUTION: A PWM controlling main-section is for outputting a pulse train Ps for PWN-controlling according to the respective input signals of voltage command V* and frequency command f*, and is composed of a data table selecting means 1, a PWM data reading-out means 2, and a PWM pattern data memory 3. The internal section of an MPU has function for generating the output of address command AV for selecting data tables 31∼364 arranged in the internal section of said memory 3, and a voltage table 11, a comparing means 12, a discriminating means 13, and address determining means 14∼15 are arranged. Besides, a PWM processor is also provided with a reading-out storage, and a frequency divider 21, an address counter 22, a mask counter 23, and a mask 24 are arranged. Then, the voltage of high resolution can be generated.