NOVELTY - A heat exchanger (11) exchanges heat from a reformed gas comprising hydrogen as a main component, to a heating medium (12). The water in the heating medium is converted into vapor, stored in a vapor storage tank (13) and supplied along with an oxidizing agent through a water vapor feed pipe (42) to gas containing gaseous fuel of hydrocarbon group, to generate mixed gas.    USE - Hydrogen manufacturing apparatus for fuel cell systems.    ADVANTAGE - Since the heat collected with the heat exchanger is utilized for preheating mixed gases the fuel heat utilization is improved. Compact size can be achieved because the CO shift catalyst and CO selective oxidation catalyst are connected and integrated with the heat exchanger.    DETAILED DESCRIPTION - The mixed gas is reformed by a modification catalyst (6) and combustion catalyst (5) to produce the reformed gas containing hydrogen as the main component. A carbon monoxide (CO) shift catalyst (7) and a CO selective oxidation catalyst (8) to reduce the CO concentration in the reformed gas, are equipped inside a cylindrical drum (15). The heating medium and the heat exchanger are placed inside the drum. The lower end of the drum equipped with reformed gas outflow path is closed. The modification catalyst and combustion catalyst are arranged between the peripheral surface of the drum and internal circumference surface of an outer pipe (31). The drum penetrates into the outer pipe top plate and water vapor insertion opening. The flow direction of the oxidizing agent and water vapor fed into the outer pipe, is reversed at the outer pipe edge portion. The oxidizing agent and water vapor mixed with the hydrocarbon group gaseous fuel to produce the mixed gas. A pressure controller is installed in the water vapor feed pipe.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of the hydrogen manufacturing apparatus. (Drawing includes non-English language text).    Combustion catalyst (5)    Modification catalyst (6)    CO shift catalyst (7)    CO selective oxidation catalyst (8)    Heat exchanger (11)    Heating medium (12)    Vapor storage tank (13)    Cylindrical drum (15)    Outer pipe (31)    Water vapor feed pipe (42)