A controller is formed as one chip, and controls a voltage regulator that supplies a power supply voltage to a CPU. The controller includes: an input unit for receiving a monitor voltage for monitoring the power supply voltage applied to the CPU; a control unit for detecting that the power supply voltage is decreased to a target voltage by the monitor voltage with the voltage regulator being in OFF state in a discharge mode; and an output unit for outputting a result signal indicating to make transition to a normal mode, when the power supply voltage has reached the target voltage. The control unit includes a calculation circuit, which is operated in accordance with a program. The calculation circuit is provided between the input unit and the output unit.