PURPOSE: To prevent an overcurrent, an abnormal oscillation from occurring at the time of starting by providing a switching control circuit for gradually varying the ON duty of both switching elements at the time of starting and composing to have a predetermined dead OFF time.

CONSTITUTION: An inverter device comprises switching elements Q1, Q2, a capacitor C0, and a load circuit L made of a load lamp l, etc., and an AC output is controlled by varying the width of the ON zones of the elements Q1, Q2. Thus, when the element Q1 is turned ON at the time of starting and an ON zone is then presented at the element Q2, nonsymmetrical AC waveforms that positive and negative side waveforms are not equal are formed by differentiating both the ON zones, and the AC waveforms are applied through the capacitor C0 to the load circuit L. Then, the ON zone of the element Q2 is gradually increased to gradually increase the AC output, thereby softly starting it.