A DC-DC converter including a power supply supplying direct current (DC) to an inductor, a switching device controlling the supply of DC from the power supply to the inductor by switching between a conductive state and a disconnected state according to a modulation signal, a signal output device generating the modulation signal for increasing or decreasing a period of the conductive state of the switching device, wherein the signal output device increases or decreases a duty ratio of the modulation signal to increase or decrease the period of the conductive state of the switching device, and a delay device controlling an increase of a duty ratio of the modulation signal, wherein the signal output device outputs the modulation signal with the controlled duty ratio to the switching device, thereby delaying the switching device from reaching a conductive state in which the duty ratio is a value of 1.