The invention discloses a control circuit of a switching power-supply device. The control circuit of a switching power-supply device that converts a first DC voltage supplied from an input power source into a second DC voltage by turning on/off a switching element connected between the input power source and an inductor and outputs the second DC voltage. The control circuit includes a drive circuit that, when a control signal to turn on the switching element is received, drives the switching element by supplying a plurality of drive voltages starting in order from a lowest drive voltage amongthe plurality of drive voltages, to a control terminal of the switching element.