A switching DC-DC converter includes: an output voltage detecting unit configured to detect a DC output voltage; an error amplifying unit configured to compare the detected output voltage and a reference voltage and configured to supply an amplified error signal between the detected output voltage and the reference voltage to the pulse width modulating unit; and a single oscillating unit connected to an output of the output voltage detecting unit and an output of the error amplifying unit and operable on a first oscillating mode and a second oscillation mode. The oscillating unit on the first oscillating mode controls a switching frequency of the power switch based on the detected output voltage. The oscillating unit on the second oscillating mode controls the switching frequency of the power switch based on the amplified error signal.