A circuit for detecting a power-on voltage of power supply encompasses a voltage divider connected between a first power supply and a second power supply, the potential of the second power supply is lower than the potential of the first power supply, and a detecting circuit connected between the first power supply and the second power supply. The voltage divider includes a series circuit encompassing a diode, a first dividing resistor connected to the diode and a second dividing resistor connected between the first dividing resistor and the second power supply. The detecting circuit includes a pMOS transistor whose gate electrode is connected to a connection node between the first dividing resistor and the second dividing resistor, a source resistor connected between the first power supply and the source electrode of the pMOS transistor and a drain resistor connected to the drain electrode of the pMOS transistor and the second power supply.