PURPOSE: To reduce loss in a snubber circuit by connecting a regenerative transformer on the primary side of a main transformer for a two-stone type DC-DC converter.

CONSTITUTION: With a two-stone type ringing choke type DC-DC converter, series bodies of capacitors 9, 9a and diodes 10, 10a are connected in parallel a snubber circuits for switching elements 2, 2a for the converter, and the capacitor sides of each snubber circuit are connected to a power supply 1. The primary side of a regenerative transformer 12 for snubber energy is juxtaposed on the primary side of a main transformer 6 for the converter, and secondary and tertiary side windings for the regenerative transformer 12 are connected through diodes 13, 13a among nodes among the capacitors 9, 9a and the diodes 10, 10a and the power supply 1. Accordingly, the energy of the inductance of wirings is absorbed to the snubber capacitor 9, and the energy is recovered to the power supply 1 through the regenerative transformer 12.