A switching power source apparatus includes a high-side MOSFET 11, a ramp generator 18 to generate a ramp signal, an amplitude signal generator (second feedback controller 2) to generate an amplitude signal Comp corresponding to an amplitude of the ramp signal, and a first feedback controller 1 to control the ON timing of the high-side MOSFET 11 according to the ramp signal, a feedback signal FB, and a first reference voltage REF and control the ON width of the high-side MOSFET 11 according to the amplitude signal Comp. The ramp generator 18 controls the inclination of the ramp signal so that the ramp signal maintains a predetermined amplitude. The first feedback controller 1 controls the ON width of the high-side MOSFET 11 so that the ON width does not become narrower than a predetermined limit value.