A DC-DC converter is provided which comprises an inductance element 10
having a plurality of in-phase windings N.sub.B, N.sub.A wound around a
common magnetic core and connected to a load 5; a normal power source 16
for generating a reference voltage; a comparator 18 for comparing a
voltage produced across winding N.sub.A with reference voltage V.sub.R of
normal power souce 16 to produce an error signal. As a same electric
current I.sub.O flows through the windings N.sub.B, N.sub.A of inductance
element 10 in the opposite directions to each other to produce in
magnetic core of inductance element 10 opposed magnetic fluxes which
countervail each other and any kind of noise such as ripple and spike
noises causing voltage fluctuation.