There is provided a DC-DC converter including: a main switching element to perform an on-off operation; a first choke coil; an output capacitor; and a diode module. The diode module includes a first series circuit which includes an auxiliary switching element and a resonant capacitor, and a second series circuit which includes a flywheel diode and a resonant coil, wherein the first series circuit and the second series circuit are connected in parallel to each other. The DC-DC converter reduces the switching loss, deals with an extensive range of input and output voltage variation, and accommodates easy modifications from conventional circuits.