A constant voltage power supply circuit including: a differential operation type amplifier, of which a first input terminal is supplied with a reference signal, and of which a second input terminal is supplied with a feedback signal. The amplifier outputs a first control signal responsive to a difference between the reference signal and the feedback signal. An output voltage detection circuit detects an output voltage of the output transistor and applies the detected voltage as the feedback signal to the second input terminal of the amplifier. A first capacitor of which one end is connected to the output portion of the output transistor; and a first control circuit, of which a first input terminal is connected to a first output terminal of the amplifier, of which a second input terminal is connected to another end of the first capacitor, and of which an output terminal is connected to a control input terminal of the output transistor.