A switching power-supply circuit includes a transformer, a first switching element, a first rectifying/smoothing circuit generating a first output voltage by rectifying and smoothing the output of a first secondary winding, a second rectifying/smoothing circuit generating a second output voltage by rectifying and smoothing the output of a second secondary winding, a first feedback circuit generating a feedback signal according to the first output voltage, and a first switching control circuit. When the voltage of the second secondary winding is greater than the second output voltage and the second output voltage is less than the voltage of a reference-voltage circuit, a second rectifier circuit turns on a rectifier switch element, and stabilizes the second output voltage by controlling the number of pulses per unit time in a pulse current flowing through the second rectifier circuit.