In a switching power supply apparatus, multiplier 9 multiplies error voltage Verr generated in voltage error amplifier 8 and input voltage Vin to generate first threshold signal Vth1 in-phase with and similar to input voltage Vin and having an amplitude proportional to error voltage Verr. Second threshold signal generator circuit 14 generates second threshold signal Vth2 from first threshold signal Vth1. Switching device 7 is turned on and off so that the inductor current may change between first and second threshold signals Vth1 and Vth2. The switching frequency is detected and the proportional factor of first and second threshold signals Vth1 and Vth2 is changed to control the average switching frequency almost at a constant value for reducing the high frequency noises and the switching losses. The switching power supply apparatus facilitates reducing the noises and losses, improving the power factor thereof, and preventing the response performances thereof from being impaired.