A PWM inverter includes a plurality of arms connected in parallel with a d.c. power source. Each arm is constituted by an upper arm and a lower arm each having a switching element. A plurality of switching control signals are continuously and alternately applied to one and the other of the two switching elements constituting the same arm respectively. In the PWM inverter, shunt resistors are connected between a minus terminal of the d.c. power source and the lower arms respectively. The PWM inverter further comprises a waveform command generating circuit generating commands representative of current waveforms to be supplied to a load, a carrier wave generating circuit and sample-hold circuits. Each of the sample-hold circuits samples and holds a terminal voltage of the associated shunt resistor in synchronism with the period of the carrier wave generated from the carrier wave generating circuit and at specific timing in a conduction period of the associated switching element.