An electric power converter includes a control unit outputting a PWM signal, a bridge circuit producing AC electric power supplied to a motor by turning semiconductor switching devices in the bridge on and off in response to PWM signals, a cut off unit cutting the PWM signals off from the bridge circuit in response to a gate signal, and a monitoring unit generating a test signal for checking the cut off unit. The cut off unit includes a switching circuit switching between the test signal and an external cut off signal, and a delay circuit that delays the output of the switching circuit. The arrangement enables the electric power converter to monitor as to whether the cut off unit is abnormal without stopping the operation of the electric power converter.