A DC-DC converter of multi-output type is provided wherein a primary winding 5a is wound around core halves 5g, 5h of a transformer 5 between first and second secondary windings 5b, 5c of transformer 5 also concentrically wound around core halves 5g, 5h to form an electromagnetic sparse coupling between first and second secondary windings 5b, 5c. When on-off operation of first and second primary MOS-FETs 2, 3 generates first and second DC outputs V.sub.O1, V.sub.O2, the electromagnetic sparse coupling can reduce, attenuate or relax serge voltage induced on first secondary winding 5b. This restrains or controls potential increase in first output voltage V.sub.O1 resulted from serge voltage through first rectifying smoother 9 under the light- or no-load condition to control fluctuation in second output voltage V.sub.O2 through second rectifying smoother 17 without restricting transmission of electric power from the primary to the secondary side making use of feedback control to primary control circuit 14 in order to generate stable first and second DC output voltages V.sub.O1 and V.sub.O2 throughout the entire loaded and unloaded range.