A power-supply voltage sensing circuit includes a switch circuit having an input connected to a power supply and an output connected to a main circuit, a first circuit that outputs a first signal controlling ON/OFF of the switch circuit in accordance with a power-supply voltage supplied by the power supply, a second circuit that delays the first signal and outputs the delayed first signal as a second signal, a first transistor that outputs a first voltage in accordance with the second signal from the second circuit, a third circuit that outputs a reference voltage when supplied with the power-supply voltage, and a comparison circuit that outputs a third signal that controls whether or not the main circuit is operated in accordance with the first voltage and the reference voltage.