PURPOSE: To contrive to lower cost by obtaining a main-circuit voltage information on the level of a logic circuit isolated from a main circuit to make V/F converter, A/D converter, photocoupler, etc., unnecessary and to contrive to downsize the circuit and to reduce a heat generation by diminishing a voltage dividing resistance.

CONSTITUTION: The title inverter apparatus comprises a switching regulator 2 having a switching circuit 2b, transformer 2a, rectifier 2c for control power supply and smoothing circuit 2d for control power supply, an oscillation frequency detection means 2e provided between the transformer 2a and rectifier 2c for control power supply to detect the oscillation frequency of the switching regulator 2 by dividing voltage with a resistance and a control circuit 5 for conducting the control of the inverter apparatus on the basis of a signal detected in the oscillation frequency detection means 2e.