PURPOSE: To provide a highly efficient PWM control voltage type inverter suitable for frequent start/stop operation which does not cause increase of power consumption and in which excessive current flow due to residual voltage is prevented at the time of starting.

CONSTITUTION: An interlock circuit 14 controls a relay amplifier 15 based on an operational signal to connect a resistor 9 in parallel with a capacitor 8 during stoppage whereas disconnect the resistor 9 from the capacitor 8 upon provision of an operational command through a relay 16 thus starting the operation. When the residual voltage of a voltage dividing resistor 12 is higher than the set value of a comparator 13, the resistor 9 is not disconnected even upon provision of the operational command and the operational command is blocked from being fed to a control circuit 11 thus preventing the operation from starting.