Abstract: An inverter apparatus comprises a bridge circuit composed of a combination of a plurality of switching transistors and a microprocessor controlling turning on and turning off of these switching transistors. Patterns of combinations of ON and OFF states of respective switching transistors obtained based on the theory of PWM (pulse width modulation) are stored in a first ROM of microprocessor. Transition of the pattern for each range of 0.degree.-30.degree. in electrical angle is stored in a second ROM in the sequence of periods subdivided from the range. Data of the time during which the pattern to be held for each period is stored in a third ROM. The microprocessor sets the holding time data in a timer, and also outputs the ON/OFF pattern, thereby turning on or turning off of each switching transistor is controlled in accordance with the count of this timer and the ON/OFF pattern. By repeating this cycle, a switching signal which continues during one cycle of AC (range of 0.degree.-360.degree.