A DC-DC converter apparatus comprising: a metal base; a transformer which performs power conversion; a rectifier element (S1, S2) which controls input and output current of the transformer; a drive circuit board to which a drive circuit to drive the rectifier element (S1, S2) is mounted; a high-voltage circuit which includes a plurality of switching elements, (H1-H4) and is connected to a primary side of the transformer; a low-voltage circuit which includes the rectifier element (S1, S2), and is connected to a secondary side of the transformer; and a high-potential-side metal conductor (402A, 402B) which connects an output terminal on the secondary side of the transformer and a high-potential-side terminal of the rectifier element (S1, S2); wherein the rectifier element (S1, S2) is arranged on the metal base to be capable of heat conduction, the drive circuit board is arranged to have a predetermined interval with respect to the metal base, wherein a drive signal wiring pattern configured to supply a drive signal to a drive signal terminal of the rectifier element (S1, S2), a high-potential-side main current wiring pattern configured to supply a main current to the high-potential-side terminal of the rectifier element (S1, S2), and a low-potential-side main current wiring pattern configured to supply the main current to a low-potential-side terminal of the rectifier element (S1, S2) are formed in the drive circuit board, the output terminal of the secondary side of the transformer is connected to one end of the high-potential-side metal conductor (402A, 402B), other end of the high-potential-side metal conductor (402A, 402B) is connected to the high-potential-side main current wiring pattern, and the high-potential-side main current wiring pattern is connected to the high-potential-side terminal of the rectifier element (S1, S2). a metal base; a transformer which performs power conversion; a rectifier element (S1, S2) which controls input and output current of the transformer; a drive circuit board to which a drive circuit to drive the rectifier element (S1, S2) is mounted; a high-voltage circuit which includes a plurality of switching elements, (H1-H4) and is connected to a primary side of the transformer; a low-voltage circuit which includes the rectifier element (S1, S2), and is connected to a secondary side of the transformer; and a high-potential-side metal conductor (402A, 402B) which connects an output terminal on the secondary side of the transformer and a high-potential-side terminal of the rectifier element (S1, S2); wherein the rectifier element (S1, S2) is arranged on the metal base to be capable of heat conduction, the drive circuit board is arranged to have a predetermined interval with respect to the metal base, wherein a drive signal wiring pattern configured to supply a drive signal to a drive signal terminal of the rectifier element (S1, S2), a high-potential-side main current wiring pattern configured to supply a main current to the high-potential-side terminal of the rectifier element (S1, S2), and a low-potential-side main current wiring pattern configured to supply the main current to a low-potential-side terminal of the rectifier element (S1, S2) are formed in the drive circuit board, the output terminal of the secondary side of the transformer is connected to one end of the high-potential-side metal conductor (402A, 402B), other end of the high-potential-side metal conductor (402A, 402B) is connected to the high-potential-side main current wiring pattern, and the high-potential-side main current wiring pattern is connected to the high-potential-side terminal of the rectifier element (S1, S2).