NOVELTY - A fuel cell system has fuel cell equipped with oxidizing agent electrode and fuel electrode, fuel gas supply unit to supply fuel gas to fuel electrode, oxidizing-agent gas supply unit to supply oxidizing-agent gas to the oxidizing agent electrode, carbon monoxide oxidation gas supply unit to supply the gas for carbon monoxide oxidation to the fuel electrode, and control unit to control the flow rate of gas for carbon monoxide oxidation at preset condition.    USE - Fuel cell system is used for generation of electric power for factory, hospital, home and motor vehicles.    ADVANTAGE - The fuel cell system suppresses fall of carbon monoxide proof property of catalyst of fuel electrode. Carbon monoxide oxidation removal of fuel electrode is promoted during starting of electric power generation of fuel cell system.    DETAILED DESCRIPTION - A fuel cell system has fuel cell equipped with oxidizing agent electrode and fuel electrode, fuel gas supply unit to supply fuel gas to fuel electrode of the fuel cell, oxidizing-agent gas supply unit to supply oxidizing-agent gas to the oxidizing agent electrode, carbon monoxide oxidation gas supply unit to supply the gas for carbon monoxide oxidation to the fuel electrode of the fuel cell, and control unit to control the flow rate of the gas for carbon monoxide oxidation supplied to the fuel electrode. The supplying ratio of gas for carbon monoxide oxidation with respect to the amount of carbon monoxide contained in the fuel gas at the side of the fuel electrode control is controlled (S202) during stopping electric power generation of the fuel cell system, to more than the supplying ratio of gas for carbon monoxide during electric power generation, by the control unit. INDEPENDENT CLAIMS are included for the following:    (1) method for stopping electric power generation of fuel cell system; and    (2) method for stopping and storage of electric power generation of fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows the flowchart of procedure for stopping of electric power generation of the fuel cell system. (Drawing includes non-English language text)    Removal of electric current (S201)    Increasing of supply ratio of air for carbon monoxide oxidation (S202)    Stopping of air to oxidizing agent electrode (S203)