Provided is a boost DC-DC converter where electric power to be supplied to a booster circuit is supplied from a power supply and from boosted electric power of the booster circuit which can be actuated at a low voltage. The boost DC-DC converter has a structure in which: a switching device is provided between the power supply and a boosted output of the booster circuit; a storage capacitor for storing electric power to be inputted to the booster circuit and for operating the booster circuit for a predetermined length of time using the stored electric power is additionally provided; and in a case where the booster circuit can generate boosted electric power even when the switching device is turned off, the switching device is turned off.