A switching power supply device has a reference voltage generator for generating a reference voltage, a ripple injector for generating a ripple by use of a pulse voltage indicating the on/off state of a switching element and injecting the ripple into the reference voltage, an integrated voltage generator for generating an integrated voltage commensurate with the integrated value of the pulse voltage throughout its on/off-duty periods, a subtractor for lowering according to the integrated voltage the reference voltage before injection of the ripple or the supply voltage to a buffer that feeds the ripple injector with the pulse voltage after making its pulse height constant, a comparator for comparing a feedback voltage with the reference voltage after injection of the ripple, and a switching controller for generating an output voltage from an input voltage by non-linear control by turning on/off the switching element according to the output of the comparator.