A switching power source control circuit comprising a comparator, a thin-out-processed pulse generator, a thinned-pulse detector, and a reset speed regulator, wherein: the comparator compares an output signal of an error amplifier with a variable reference voltage generated by the reference voltage regulator to generate a signal for performing thin-out operation in accordance with a voltage difference between the output signal of the error amplifier and the reference voltage; the thin-out-processed pulse generator generates thin-out-processed pulses on the basis of the output signal of the comparator; the thinned-out pulse detector detects the generation of thinned-out pulses or driving pulses while always monitoring the thin-out-processed pulses generated from the thin-out-processed pulse generator, and changes the reference voltage of the reference voltage regulator in the case where the thin-out rate is in a range of from 0 to 1/2 in the direction to make it difficult to perform thin-out operation to thereby prevent continuation of thin-out operation whenever one thinned-out pulse is detected; and the reset speed regulator resets the reference voltage of the reference voltage regulator to an initial value in accordance with the output signal of the error amplifier.