NOVELTY - A burner (16) supplies combustion gas to a combustion gas flow path (12) covering a modifier (10). A fuel supply unit (32) supplies fuel to the flow path. An evaporation unit (28) covers the outer side of the flow path and a temperature sensor (33) is arranged in the downward direction of the evaporation unit to detect temperature of the water collected in the evaporation unit.    USE - For production of hydrogen gas supplied to fuel cell system (claimed).    ADVANTAGE - The terminal efficiency of the hydrogen generation apparatus is improved, by regulating supply amount of fuel and air based on detected temperature. The variation in the concentration of the carbon monoxide in the reformed gas is reduced. Ensures stable production of hydrogen.    DETAILED DESCRIPTION - The modification unit generates reformed gas containing hydrogen by water-vapor modification reaction of raw material containing hydrocarbon compound. The combustion gas flow path is provided on the outer side of the modification unit. The evaporation unit has upper and lower evaporation chambers (18,22) provided with water inlets. A controller reduces the supply amount of gaseous fuel and air selectively to the burner, when the detected temperature is more than preset value. The supply amount of water or water-vapor to the upper evaporation chamber is regulated based on the temperature sensor. A heat-conducting fin (34) is arranged in the outer surface of the evaporation unit to exchange heat of the water with the combustion gas.    INDEPENDENT CLAIMS are also included for the following:    (1) fuel cell system which generates electric power by using gaseous fuel containing hydrogen and oxidizing-agent gas; and    (2) hydrogen generation method which involves regulating supply amount of gaseous fuel and air to the burner, based on the temperature sensor detecting temperature of the water collected in the evaporation unit.    DESCRIPTION OF DRAWING(S) - The figure shows a sectional view of the hydrogen generation apparatus. (Drawing includes non-English language text).    modifier (10)    combustion gas flow path (12)    burner (16)    evaporation chambers (18,22)    evaporation unit (28)    fuel supply unit (32)    temperature sensor (33)    heat-conducting fin (34)