NOVELTY - A fuel cell system (1) comprises fuel cell (2) which generates electrical energy according to electrochemical reaction of oxidizing agent gas and fuel gas, modifier (3) which modifies fuel gas made of hydrocarbon by partial oxidation reformation reaction and steam reformation reaction, evaporator (4) which generates steam for heating water and using for steam reformation reaction,1st combustor (6) which produces 1st combustion gas, 2nd combustor (7) which produces 2nd combustion gas, and control unit (8).    USE - A fuel cell system.    ADVANTAGE - In system startup, overheating of modifier can be suppressed and early supply of steam to modifier can be achieved.    DETAILED DESCRIPTION - A fuel cell system (1) comprises fuel cell (2) which generates electrical energy according to electrochemical reaction of oxidizing agent gas and fuel gas, modifier (3) which modifies fuel gas made of hydrocarbon by partial oxidation reformation reaction and steam reformation reaction, and supplies reformed fuel gas to fuel cell, evaporator (4) which generates steam for heating water and using for steam reformation reaction, and supplies generated steam to modifier, 1st combustor (6) which produces 1st combustion gas by combustion reaction of discharge fuel discharged from fuel cell, 2nd combustor (7) which produces 2nd combustion gas by combustion reaction of discharge fuel discharged from fuel cell, and is positioned in different position from 1st combustor, and control unit (8) which controls switching of implementation of combustion reaction in 1st combustor and implementation of combustion reaction in 2nd combustor. Modifier contains 1st combustion gas so that heat transfer is possible. Evaporator contains both 1st combustion gas and 2nd combustion gas so that heat transfer is possible. When control unit implements combustion reaction in 1st combustor, partial oxidation reformation reaction in modifier is implemented. When temperature of modifier exceeds predetermined temperature, combustion reaction in 1st combustor is stopped and implementation of combustion reaction in 2nd combustor is implemented.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the fuel cell system. (Drawing includes non-English language text).    Fuel cell system (1)    Fuel cell (2)    Modifier (3)    Evaporator (4)    1st combustor (6)    2nd combustor (7)    Control unit (8)