A detection circuit is provided to output a feedback signal and a adjustment current when a voltage of a high-voltage side main terminal of a semiconductor switching device is equal to or higher than a preset threshold value in a period in which a gate drive circuit turns off the semiconductor switching device to cut off a current, a control circuit diagnoses a state of the semiconductor switching device or controls a signal to be outputted to the gate drive circuit, on the basis of the feedback signal, and a gate current, which is an output of the gate drive circuit, is adjusted by the adjustment current.