Abstract: An inverter apparatus operatable over an extended output frequency range having an increased upper limit with error contained in the output voltage being suppressed by eliminating dispersions of PWM pulse signals. A PWM command pulse signal and an output voltage detection signal derived from the output of the inverter are compared straightforwardly with each other for determining difference therebetween on the basis of which error contained in the inverter output voltage is canceled. An isolation device for isolating electrically a low-voltage-rated control circuitry and a high-voltage-rated main circuitry from each other is inserted between a PWM command pulse signal generating circuit and a pulse width correcting circuit.