The fuel cell power generation system of present invention can supply the air pole of a fuel cell with a clean air free from impurities, by providing at least one or more humidification filters kept in a wet state by a water supply means, disposed in an oxidant gas supply passage of the fuel cell body. As a result, the cell output properties can be improved by preventing the decrease of gas dissipation ability or the decrease of electric conductance of the solid polymer film provoked by impurities.