A piezoelectric device is connected in parallel with a diode, and outputs a power generation voltage when depressed. When the power generation voltage exceeds a first threshold voltage, a load switch control circuit makes a load switch be conductive, and when the generated voltage becomes lower than a second threshold voltage, the load switch is cut off. Further, when depression is released, the piezoelectric device is discharged by the diode such that the amount of charge remaining in the piezoelectric device becomes zero.