NOVELTY - The hydrogen production apparatus has raw material supply portion (6), water supply portion (7), hydrogen generation portion (1), combustion air supply portion (12), modification temperature measurement portion (3) and control portion (9) continues supply of raw material and water during apparatus stop operation. Output of portion(s) (6,7,12) is controlled, so that temperature of modification reaction portion (2) reduces.    USE - For fuel cell system (claimed) for generating electric power.    ADVANTAGE - The hydrogen generation apparatus reduces temperature of modification reaction portion rapidly, easily and reliably.    DETAILED DESCRIPTION - The hydrogen production apparatus has raw material supply portion (6), water supply portion (7), hydrogen generation portion (1) having modification reaction portion (2), heating portion for supplying required heat for modification reaction to portion (2), combustion air supply portion (12), modification temperature measurement portion (3) and control portion (9). Portion (6) supplies raw material containing organic compound having carbon and hydrogen. Portion (2) produces hydrogen rich gas by modification of raw material and water. Portion (12) supplies air to heating portion. Portion (3) detects temperature of modification catalyst material or temperature of gas passed through portion (2). Portion (9) controls output of portions (6,7,12). Gas emitted from portion (1) is returned from gas supply place to heating portion. Portion (9) continues supply of raw material and water during apparatus stop operation. The output of portion(s) (6,7,12) is controlled, so that temperature of portion (2) reduces. The supply of water and raw material are stopped, when detection temperature in portion (3) is less than the predetermined reference temperature.    An INDEPENDENT CLAIM is included for fuel cell system.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic diagram of the hydrogen generation apparatus. (Drawing includes non-English language text).    hydrogen generation portion (1)    modification reaction portion (2)    modification temperature measurement portion (3)    raw material supply portion (6)    water supply portion (7)    control portion (9)    air supply portion (12)