A fuel cell power generation system including a reforming reactor for reacting a fuel with water to produce a hydrogen-rich reformed gas including carbon monoxide; a CO shift reactor for carrying out a CO shift reaction to decrease the concentration of carbon monoxide in the reformed gas; a CO removal reactor for oxidizing carbon monoxide in the reformed gas to carbon dioxide; and a fuel cell for generating electric power by reaction of the reformed gas with a gaseous oxidizing agent. Processors determine output required of the fuel cell and a proper space velocity for reformed gas entering the CO removal means, based on input values for the amount of the reformed gas fed to the CO removal means and the determined output required of the fuel cell.