A determining unit determines the state of the microprocessor. A setting unit sets a power supply voltage to be supplied to the microprocessor according to the state of the microprocessor determined by the determining unit. A power supply circuit supplies the power supply voltage set by the setting unit, to the microprocessor via a power supply line. The determining unit determines repeatedly the state of the microprocessor at preset timing, and the setting unit resets the power supply voltage every time the determination is performed by the determining unit.