A DC-DC converter having a transformer having a primary winding and a secondary winding; means for supplying DC input voltage to the primary winding; at least one switching element connected between the DC input voltage supplying means and the primary winding; rectifying means; at least one saturable reactor having a first winding and a second winding, the first winding being connected between one end of the secondary winding which is positive while the switching element is in a turn-on state and the rectifying means; and reset control circuit means connected to the second winding of the saturable reactor for supplying reset voltage thereto in response to output voltage of the rectifying means. The first and second windings have such polarities that the reset voltage can reset the saturable reactor during a turn-off period of the switching element. This DC-DC converter enjoys less temperature rise in the saturable reactor and a lower level of noise generation.