PURPOSE: To prevent an irregular magnetization from occurring by providing an irregular magnetization detection circuit having an addition circuit and an integration circuit in a controlling circuit for a pulse-width modulation inverter.

CONSTITUTION: A controlling circuit for a pulse-width modulation inverter applies output signals 1∼4 from two distributors 19∼20 to the bases of transistors Tr1∼Tr4 to drive them, regulates a voltage value applied to the input of a level regulator 13 to move the output signal of an error amplifier 12 in positive or negative direction, thereby removing asymmetrical component in a normal operation. In this case, an output from an irregular magnetization detector 14 is applied to the regulator 13. The detector 14 has an adder 21 which inputs the outputs from first and second comparators 15, 16, and an integrator 22. Thus, a closed loop of the regulator 13, the comparator 15, the detector 14 and the regulator 13 is composed to perform an irregular magnetization preventing operation.