A DC conversion apparatus includes a switch that converts a DC voltage of a DC power source to a high-frequency voltage by being turned ON/OFF via a primary winding of a transformer, a synchronous rectifying circuit that performs synchronous rectification of a high-frequency voltage generated at a secondary winding, a smoothing circuit that smoothes a rectified output of the synchronous rectifying circuit by a smoothing reactor and a smoothing capacitor, and outputs a DC voltage, a capacitor that stores via a diode, energy stored in the smoothing rector due to a current backflow of the synchronous rectifying circuit under light load condition, a switch that is turned ON in synchronization with the switch, and returns the energy stored in the capacitor via the transformer to a primary side thereof, and a control circuit that turns ON/OFF the switch.