A constant voltage circuit is disclosed that includes a constant voltage generator circuit part converting an input voltage into a predetermined constant voltage in accordance with an externally input control signal and outputting the constant voltage; a first capacitor connected to the output end of the constant voltage generator circuit part; a second capacitor charging the first capacitor; and a switch circuit part controlling charging and discharging of the second capacitor in accordance with the control signal. The switch circuit part charges the second capacitor and blocks the discharging of the second capacitor to the first capacitor when the constant voltage generator circuit part is caused to stop outputting the constant voltage by the control signal, and stops applying the input voltage to the second capacitor and charges the first capacitor when the constant voltage generator circuit part is caused to start outputting the constant voltage by the control signal.