PURPOSE: To prevent the consumption of a regenerative current by a load and to avoid the deterioration of a current wave form, in an inverter wherein a d.c. power source is pulse-modulated and an a.c. current of any frequency is caused to flow in the load circuit.

CONSTITUTION: While a first switching circuit 21 turns on and off according to a first PWM signal 1 whose pulse width is modulated by half a cycle like a sine curve, a second switching circuit 22 turns on and off reversely and a fourth switching circuit 24 is kept in on state. And, while a third switching circuit 23 turns on and off according to a second PWM signal 2 which is generated half a cycle after the first PWM signal 1 is generated, the fourth switching circuit 24 turns on and off reversely and the second switching circuit 22 is kept in on state. When the PWM signal is switched, either one of the second and the fourth switching circuits 22 and 24 is in on state and the other turns on and off and an a.c. current very much like a sine wave is caused to flow in a winding L1 in order to cause a regenerative current of the winding L1 of a motor M to flow.