A constant voltage circuit that is capable of realizing high speed response with respect to an abrupt change in an input voltage or a load current is disclosed. The constant voltage circuit includes a first error amplifier with a high direct current gain and a second error amplifier with high speed responsiveness with respect to a change in an output voltage. The constant voltage circuit uses the first and second error amplifiers to conduct operation control of an output voltage control transistor in response to a change in the output voltage.