NOVELTY - A hydrocarbon raw material is contacted with water in catalyst layer, and steam modification is carried out to obtain hydrogen. The heating temperature of catalyst is increased until the catalyst inlet-port temperature reaches more than reference temperature. Water and raw material are supplied at specific feed rates while the inlet-port temperature satisfies a preset relationship. The temperature of catalyst is adjusted to temperature at steady operation. The feed rates of water and raw material, and inlet-port temperature satisfy preset relationships.    USE - Starting method of hydrogen generator used in fuel cells and petroleum refineries.    ADVANTAGE - The method enables economical hydrogen production without catalyst deterioration by coke precipitation. During steady operation, the steam supply ratio is lowered, which suppresses energy loss by excess steam.    DETAILED DESCRIPTION - A hydrocarbon raw material having an initial boiling point of 100 degrees C or more is contacted with water in a fixed-bed catalyst layer, and steam modification is carried out to obtain hydrogen. The heating temperature of catalyst layer is increased until the catalyst layer inlet-port temperature reaches more than reference temperature (T1). Water and raw material are supplied at feed rates (X,Y: g/hour) while the catalyst layer inlet-port temperature (T) satisfies a preset relationship. The temperature of catalyst layer is adjusted to the temperature at steady operation. The feed rate (X) of water, the catalyst layer inlet-port temperature (T), and the feed rate (Y) of raw material satisfy preset relationships given by, T = T1-T2, X is greater than (X4/Y4x Y), and Y less than or equal to Y4, where T2 is reference temperature, X4 is feed rate (g/hour) of water in hydrogen generation operation, and Y4 is feed rate (g/hour) of raw material in hydrogen generation operation. The active-metal component of the fixed-bed catalyst layer contains ruthenium, rhodium and/or platinum. The hydrocarbon is lamp oil.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the hydrogen generator.    Raw-material vaporizer (EV110)    Mixer (M130)    Modifier (R140)    Raw-material tank (T110)    Water tank (T120)