Back pressure is applied to a liquid fuel stored in a fuel storage unit by
a pressure application unit, and a liquid fuel vaporization membrane that
vaporizes the liquid fuel to thereby supply the vaporized fuel gas to an
anode is formed by a nonporous membrane. Backed by this, the liquid fuel
can be prevented from leaking out to the anode, so that the concentration
of the liquid fuel can be increased to an optimum level.