A separator is provided with a substrate portion having a predetermined
concave-convex shape, an underlying coating layer formed on the substrate
portion, a first coating layer coating the substrate portion and the
underlying coating layer, and a second coating layer formed thereon. The
second coating layer, which is formed from carbon materials, is
sufficiently electrically conductive and protects the underlying layers.
The first coating layer is formed from a low-melting-point metal
subjected to a melting process. The melting process is a process of first
conducting heating at such a temperature that melts the low-melting-point
metal but does not melt the substrate portion and the underlying coating
layer and then conducting cooling. Thus, in the first coating layer, the
crystal grain size of the metal is increased and thus the grain boundary
density is reduced.