Provided is a power supply voltage monitoring circuit capable of accurately detecting a power supply voltage with a small circuit scale and low power consumption. The power supply voltage monitoring circuit includes: a signal output circuit configured to output a signal voltage representing saturation characteristics with respect to an increase in power supply voltage; and a signal voltage monitoring circuit configured to output a signal representing that the signal voltage of the signal output circuit is normal, the signal voltage monitoring circuit including: a PMOS transistor including a gate connected to an output terminal of the signal output circuit; a first constant current circuit connected to a drain of the PMOS transistor; and an inverter including an input terminal connected to the drain of the PMOS transistor.