NOVELTY - A solid oxide fuel cell system (100) comprises air supply device for modification (10) which supplies air for modification, material supply device (12) which supplies raw material, modifier (14) which produces hydrogen-containing gas using air for modification supplied from air supply device and raw material supplied from material supply device, solid oxide fuel cell (20) provided with anode (16) and cathode (18), anode off-gas recycle path (22) for supplying anode off-gas discharged from anode to modifier, and anode off-gas supply device (24).    USE - A solid oxide fuel cell system for electric power generation (claimed).    ADVANTAGE - Carbon cannot easily precipitate in inner side of modifier. Excessive modifier temperature increase is prevented.    DETAILED DESCRIPTION - A solid oxide fuel cell system (100) comprises air supply device for modification (10) which supplies air for modification, material supply device (12) which supplies raw material, modifier (14) which produces hydrogen-containing gas using air for modification supplied from air supply device and raw material supplied from material supply device, solid oxide fuel cell (20) provided with anode (16) and cathode (18), anode off-gas recycle path (22) for supplying anode off-gas discharged from anode to modifier, anode off-gas supply device (24) which adjusts amount of anode off-gas supplied to modifier through anode off-gas recycle path, anode off-gas heat radiator (26) which is provided in anode off-gas recycle path, thermally radiates anode off-gas, and generates condensed water, modifier temperature detector (28) which detects temperature of modifier, and controller (19) which adjusts supply amount of air for modification, supply amount of anode off-gas, and supply amount of raw material to modifier based on temperature of modifier by controlling air supply device for modification, material supply device, and anode off-gas supply device. Solid oxide fuel cell generates electric power by using hydrogen-containing gas supplied to anode and air supplied to cathode from modifier.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the solid oxide fuel cell system. (Drawing includes non-English language text).    Air supply device for modification (10)    Material supply device (12)    Modifier (14)    Anode (16)    Cathode (18)    Controller (19)    Solid oxide fuel cell (20)    Anode off-gas recycle path (22)    Anode off-gas supply device (24)    Anode off-gas heat radiator (26)    Modifier temperature detector (28)    Solid oxide fuel cell system (100)