A switching element connects/disconnects an input end to/from at least either of power supply lines. A switching element is provided between the power supply lines. One end on the low potential side of a power supply unit is connected to the switching element on the side of either of the power supply lines. One end of a capacitor is connected between the switching element and the input end. The other end of the capacitor is connected to one end on the high potential side of the power supply unit. The capacitor and the power supply unit respectively serve as operation power supplies for outputting switch signals to the switching elements. A voltage adjustment unit maintains voltage across both ends of the capacitor.