A switching power supply device wherein an input voltage is stepped-up by first and second switching elements that are driven on and off in a complementary way, thus obtaining a stabilized output voltage. The switching power supply device includes a comparator that detects fluctuation in an operating reference potential of the second switching element accompanying fluctuation in the input voltage, and a drive signal generator circuit that carries out a logical operation on an output control signal, a dead time signal, and the output signal of the comparator, thus generating first and second drive signals that determine the on-state time of the first and second switching elements.