a constant - voltage power supply circuit includes a constant - voltage output unit and an output current restriction unit . the constant - voltage output unit includes an output transistor and controls the transistor based on output voltage from the output transistor to maintain the output voltage constant . the output current restriction unit restricts output current of the constant - voltage output unit . when the overcurrent detection unit detects that current flowing through the output transistor that is an overcurrent flowing continuously for a predetermined time , the output current restriction unit executes an output current restriction operation . this configuration prevents the output voltage from decreasing after an overcurrent control operation .