According to a preferred embodiment of the present invention, a low-voltage operation constant-voltage circuit includes a band-gap reference voltage circuit including a resistor-diode series circuit as a main component. A resistor and a diode-connected bipolar transistor are connected in series to create a constant current. It also includes an output circuit connected in parallel to the resistor-diode series circuit and formed so that the same constant current as the current flowing through the resistor-diode series circuit flows. The output circuit includes a diode-connected MOS transistor, and is configured to cancel the positive temperature coefficient of the current flowing through the output circuit by the MOS transistor. With this, a stable output low-voltage of, e.g., about 0.6 V, excellent in temperature characteristics can be obtained regardless of the ambient temperature changes.