Switching power-supply device

The invention provides a switching power supply unit which can suppress the deviation of the start time of the slope compensation. The switching power supply device comprises a slope compensation circuit which is used for suppressing subharmonic oscillation according to a timing signal from the oscillation circuit (7) . The oscillating circuit (7) includes a first circuit(M1- M9, C2, Vref, 27) generating signals with a basic oscillation frequency, and a second circuit (29, 31 , 33) of the time signals generated by logic processing of the fundamental ocilalating frequency signals.