In a switching circuit apparatus, first and second capacitors apply power supply voltages to first and second drive circuits. First and second diodes are connected such that currents flow from a DC voltage source to the first and second capacitors. A resistor and a Zener diode are connected in series between a terminal and a node, such that a reverse bias voltage is applied from the terminal to the Zener diode via the resistor. A third diode is connected such that a current flows to the first capacitor from a node (N2) between the resistor and the Zener diode.