To achieve reduction in size and reduction in cost of a DC-DC converter apparatus. Rectifier elements and are installed onto a metal base, and a drive circuit board is installed to an upper part of the rectifier element. Each terminal of the rectifier elements and is soldered to the drive circuit board. Three terminals of the rectifier elements are soldered, respectively, to a drive signal wiring pattern, a high-potential-side main current wiring pattern, and a low-potential-side main current wiring pattern of the board. A pair of output terminals of a transformer is connected to at least the pair of high-potential-side main current wiring patterns using high-potential-side metal conductors.