The invention provides a short-circuit protective circuit for a constant-voltage power-supply circuit. The constant-voltage power-supply circuit can realize a short-circuit protection with a simple circuit configuration in a power-supply circuit provided with a plurality of power-supply lines. A regulator is connected to one of a plurality of power-supply lines, and a constant voltage is outputted from an output terminal of the regulator through an output line. An output voltage from the regulator is inputted to constant-voltage circuits as a reference voltage, and output constant voltages from the constant-voltage circuits are supplied to the other output lines. A voltage detection circuit is connected to the other output lines, wherein if a voltage drop occurs in any output line, a detection signal is outputted to an operation circuit, thereby turning off an output control terminal of the regulator. Accordingly, the output of the regulator is stopped so that all of the output lines are stopped all at once. The invention is cost-efficient because the invention uses only one regulator to control multiple power-supply lines.