PURPOSE: To make it possible to clean effectively the poisoned catalyst of a fuel cell by, after drawing fuel gas from a fuel gas flow system by means of feeding inert gas to the system, supplying oxidizer gas to oxidize the poisoned catalyst of fuel cell electrodes and redrawing the oxidizer gas from within the system by means of feeding inert gas again.

CONSTITUTION: At the point of time when the output voltage of a fuel cell electrode goes down below a prescribed value, the cell operation is stopped, and the gas flow system, which charges and discharged fuel to and from this single cell, is displaced by nitrogen to draw fuel gas from within the system. After that, air is sent to the fuel cell electrodes at the operating temperature of 160°C to oxidize the carbon monoxide, which has poisoned the electrode catalyst, into CO2; thus the poisoned catalyst is given a catalyzing function again. After cleaning the catalyst by supplying air, the air within the gas flow system is drawn out by means of displacing the system interior with nitrogen, thus the fuel gas is supplied again to operate the cell.