A DC--DC converter is composed of an overcurrent cut-off means connected in
series to a direct power source, primary windings of a plurality of
transformers connected in series to the overcurrent cut-off means, a
switching element connected in series to the overcurrent cut-off means and
secondary windings of a plurality of transformers connected in parallel
with each other. According to the DC--DC converter, a voltage induced on
the secondary windings are rectified and smoothed by a first rectifying
and smoothing circuit to output the smooth direct voltage to a load. When
a short-circuit test is carried out for one of the primary windings, the
overcurrent cut-off means cuts off an overcurrent flow.
