TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Conditions: The carbon-monoxide concentration in the hydrogen gas supplied to reactor (I) is 0.3-1 vol.%, the carbon-monoxide concentration in the outlet gas of reactor (I) is 500 ppm or less, and the carbon-monoxide concentration in the outlet gas of reactor (II) is 10 ppm or less. A carbon-monoxide adsorption tower filled with an adsorption agent is connected to reactor (II).    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The catalyst used for reactor (I) is a catalyst in which the carbon-monoxide removal rate becomes highest with the reaction temperature of 190-210degreesC. The catalyst used for reactor (II) is a catalyst in which the carbon-monoxide removal rate becomes highest with the reaction temperature of 120-140degreesC. The carbon-monoxide removal rate of catalyst used for reactor (I) is 95% or more, and that of reactor (II) is 98% or more. The catalyst used for reactor (I) consists of zirconia, ceria, nickel oxide, cobalt oxide (CoO,Co3O4), ferric oxide, alumina, titania, silica, and/or their complex oxides including alkali-metal oxide, alkaline-earth metal oxide, and rare-earth metal oxide. Further, metal(s) chosen from groups 4B, 6A, 7A and 8 are supported. The catalyst used for reactor (II) consists of nickel oxide, cobalt oxide (CoO,Co3O4), zirconia, ceria, alumina, titania, silica, and/or their complex oxides. Further, metal(s) chosen from groups 4B, 6A, 7A and 8 are supported. Preferred Agent: The adsorption agent consists of zeolite in which metals of groups 4B, 6A, 7A and/or 8 are supported. The metal content in the adsorption agent is 0.5-15 wt.%. The zeolite is ZSM-5 type zeolite, mordenite type zeolite, faujasite type zeolite, and/or beta-zeolite.    TECHNOLOGY FOCUS - METALLURGY - Preferred Metals: The group 4B metal is tin, group 6A metal is molybdenum and tungsten, group 7A metal is manganese and rhenium, and group 8 metal is ruthenium, platinum, palladium, nickel, iron and cobalt. The metal load of catalyst used for reactor (II) is 0.5-15 wt.%. The supported metal is ruthenium, and the ratio of ruthenium is 20-90 wt.%.