NOVELTY - A fuel cell system (100) consists of modification portion (14), selective-oxidation portion (17), air supply portion (16), hydrogen generating apparatus (1), fuel cell (2) and control portion (12). The modification portion, in which raw material and water are supplied and hydrogen-containing gas is produced by reforming reaction. The selective-oxidation portion, in which reduction of carbon monoxide concentration in the hydrogen-containing gas is carried out by selective oxidation reaction of supplied air. The air supply portion which supplies air to the selective-oxidation portion.    USE - Fuel cell system is used for solar energy power generation system and storage battery.    ADVANTAGE - The fuel cell system completely reduces carbon monoxide concentration of hydrogen-containing gas supplied to fuel cell and thermal runaway of the temperature of selective-oxidation portion. The fuel cell has excellent durability.    DETAILED DESCRIPTION - A fuel cell system consists of modification portion, selective-oxidation portion, air supply portion, hydrogen generating apparatus, fuel cell and control portion. The modification portion, in which raw material and water are supplied and hydrogen-containing gas is produced by reforming reaction. The selective-oxidation portion, in which reduction of carbon monoxide concentration in the hydrogen-containing gas is carried out by selective oxidation reaction of supplied air. The air supply portion which supplies air to the selective-oxidation portion. The hydrogen generating apparatus is provided with selective-oxidation temperature detection portion (20) for detecting temperature of selective-oxidation portion. The fuel cell generates electric power and into which oxygen-containing gas and hydrogen-containing gas in which carbon monoxide concentration is reduced, are supplied. The power generation output command value to the fuel cell is updated with respect to power generation output command value to the fuel cell and temperature detected by the temperature detecting selective-oxidation portion. The control portion which outputs the air flow amount command value to the selective-oxidation portion.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic block view of fuel cell system. (Drawing includes non-English language text)    Hydrogen generating apparatus (1)    Fuel cell (2)    Control portion (12)    Modification portion (14)    Air supply portion (16)    Selective-oxidation portion (17)    Selective-oxidation temperature detection portion (20)    Fuel cell system (100)