NOVELTY - A fuel cell system (100) comprises modification part (20) where raw material and water are supplied and produces hydrogen-containing gas by reforming reaction, modification temperature detection part (21) which detects temperature of modification part, material supply part (4) which supplies raw material according to raw material feed rate indication value to modification part, water supply part (3) which supplies water according to water feed rate indication value to modification part, and transformation part (13) which reduces carbon monoxide concentration in hydrogen-containing gas.    USE - A fuel cell system (claimed).    ADVANTAGE - Fuel cell system can determine whether amount of air supplied to hydrogen generating apparatus from air supply part is appropriate.    DETAILED DESCRIPTION - A fuel cell system (100) comprises modification part (20) where raw material and water are supplied and produces hydrogen-containing gas by reforming reaction, modification temperature detection part (21) which detects temperature of modification part, material supply part (4) which supplies raw material according to raw material feed rate indication value to modification part, water supply part (3) which supplies water according to water feed rate indication value to modification part, transformation part (13) which reduces carbon monoxide concentration in hydrogen-containing gas, transformation temperature detection part (24) which detects temperature of transformation part, selective-oxidation part (17) which reduces carbon monoxide concentration in hydrogen-containing gas reduced by transformation part, air supply part (19) which supplies air according to air feed rate indication value to selective-oxidation part, selective-oxidation temperature detection part (26) which detects temperature of selective-oxidation part, fuel cell (8) where hydrogen-containing gas and oxygen-containing gas by which carbon monoxide concentration is reduced and generated in selective-oxidation part are supplied and tracks change of electric power load of electric power supply destination, combustion part (2) which burns remaining hydrogen-containing gas not consumed by fuel cell and supplies heat required for reforming reaction of modification part, and operation-control part (16) which outputs air feed rate indication value to air supply part based on selective-oxidation temperature and does not make period preset after generating arbitrary electric power generation amount which fuel cell has, wherein fuel cell system determines if air corresponding to indication value preset is not supplied from air supply part as indicated when temperature difference with estimated selective-oxidation temperature from indication value and detected selective-oxidation temperature is beyond a predetermined temperature difference.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a fuel cell system. (Drawing includes non-English language text).    Water supply part (3)    Material supply part (4)    Transformation part (13)    Modification part (20)    Modification temperature detection part (21)