A suppressing circuit is provided with a diode of which an anode is connected to a first neutral point between a drive circuit and a control electrode of a semiconductor switch; a capacitor disposed between a cathode of the diode and a reference potential; a constant voltage circuit connected to a second neutral point between the diode and the capacitor; an adjusting resistor disposed between the constant voltage circuit and the second neutral point; and a cutoff switch disposed between a constant voltage circuit side of the adjusting resistor and the reference potential.