PURPOSE: To decrease water vapor partial pressure near the outlet of a cell to retard deterioration of an electrode by mixing exhaust gas or part of exhaust gas from a fuel cell in a gas supply line of a fuel cell through a vapor-moisture separator.

CONSTITUTION: A gas is supplied to and exhausted from a fuel cell 1 through gas supply and exhaust pipes 2 and 3 respectively to generate electric power. An exhaust gas or part of exhaust gas from the fuel gas 1 is mixed in a gas supply line 2 to circulate it through a gas supply passage 5 comprising a vapor-moisture separator 4 and a blower 6. Since the amount of water vapor exhausted from the gas exhaust pipe 3 is decreased by being removed in the vapor-moisture separator, the water vapor partial pressure in the outlet is decreased. Therefore, deterioration of a gas diffusion electrode and performance drop of fuel cell 1 caused by water vapor are retarded, and the life of the fuel cell 1 is increased.