A first surge absorber has a low resistance when a surge voltage which is greater than or equal to a first operating voltage is applied to a power supply line, and has a high resistance when the surge voltage which is greater than or equal to the first operating voltage is not applied. A detector outputs a detection signal indicating that the surge voltage is greater than or equal to the first operating voltage when the surge voltage is greater than or equal to the first operating voltage. A second surge absorber becomes a low resistance when a surge voltage greater than or equal to a second operating voltage is applied, and becomes a high resistance when a surge voltage greater than or equal to the second operating voltage is not applied.