NOVELTY - A fuel oil is supplied to modification portion containing water vapor modification catalyst and water vapor modification reaction is performed using inlet temperature of water vapor modification catalyst layer at 500 degrees C or less, to obtain gas containing hydrogen. The fuel oil contains sulfur, dibenzothiophene, aromatic content and linear aliphatic saturated hydrocarbon, and has distillation initial boiling point at 140 degrees C or more, 95 volume% of distillation point at 270 degrees C or less and distillation end point at 300 degrees C or less.    USE - Fuel oil is used for producing hydrogen (claimed) in fuel cell used as power supply of hydrogen plants in petroleum refinery.    ADVANTAGE - The hydrogen is economically produced using fuel oil by suppressed occlusion of modifier by active deterioration of modification catalyst, for long time.    DETAILED DESCRIPTION - A fuel oil is supplied to modification portion containing water vapor modification catalyst and water vapor modification reaction is performed using inlet temperature of water vapor modification catalyst layer at 500 degrees C or less, to obtain gas containing hydrogen. The fuel oil contains (in mass ppm) sulfur (0.05 or less), dibenzothiophene (0.02 or less), less than 20 volume% of aromatic content and less than 25 mass% of linear aliphatic saturated hydrocarbon, and has distillation initial boiling point at 140 degrees C or more, 95 volume% of distillation point at 270 degrees C or less and distillation end point at 300 degrees C or less. An INDEPENDENT CLAIM is included for producing hydrogen by supplying fuel oil to modification portion containing water vapor modification catalyst adhesive performing water vapor modification reaction using inlet temperature of water vapor modification catalyst layer at 500 degrees C or less.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of hydrogen production apparatus.    Analyzer (A150)    Mixer (M130)    Modifier (R140)    Fuel oil tank (T110)    Water tank (T120)