This constant-voltage circuit (1) is equipped with an overcurrent protection circuit (4). The overcurrent protection circuit is equipped with: a first sense transistor (M3) which generates a current which corresponds to an output current of an output transistor, one of the main terminals of said first sense transistor being connected to an input terminal (IN), and a control terminal of which being connected to a control terminal of the output transistor (M11); a voltage level adjustment circuit (7) which extracts a current unaffected by fluctuation in the output current of the output transistor from a main terminal of the output transistor on the output terminal (OUT) side to generate a voltage which corresponds to the voltage of the aforementioned main terminal of the output transistor on the output terminal side, and adjusts the voltage of the other main terminal of the first sense transistor so as to become equal to this generated voltage; and a protection circuit (8) which controls a control voltage according to the current generated by the first sense transistor, said control voltage being applied from an error amplifier (3) to the control terminal of an output transistor.
