A fuel gas passage, an oxygen-containing gas passage, and a coolant passage extend
through a fuel cell stack. Each of the fuel gas passage and the oxygen-containing
gas passage is formed by serially connecting passages between the first through
third fuel cell modules. The fuel gas flows through the fuel gas passage, and the
oxygen-containing gas flows through the oxygen-containing gas passage from the
first fuel cell module toward the third fuel cell module. The coolant passage is
formed by serially connecting passages between the first through third fuel modules.
The coolant flows through the coolant passage from the third fuel cell module toward
the first fuel cell module. The direction of the flow of the coolant is opposite
to the direction of the flows of the fuel gas and the oxygen-containing gas.
