To provide a control circuit for switching power supplies for accurately suppressing low voltage or overvoltage that may be produced in the output of a switching power supply.

When an undershoot occurs, not only detection output voltage Va (213) but also feedback voltage Vc (224) varies. The feedback voltage Vc (224) varies in the reversed phase to the phase of the detection output voltage Va (213) and the amount of this variation Vc is obtained by the expression of Vc=-VaR4/R3. The difference between variation in the detection output voltage Va (213) and variation in the feedback voltage Vc (224) is expressed as Va-Vc=(1+R4/R3)Va and this difference is inputted to a comparator 280. The amplitude of input signals to the comparator 280 is thereby increased to avoid the influence of the offset variation of the comparator 280.