NOVELTY - Hydrogen-production apparatus includes modifiers (103) of reaction tubes (111), which introduce mixing steam. A catalyst (115) is provided within a reaction, carries out steam reforming of the mixing steam, and promotes a hydrogen production. Thermal-medium oil retains in a shell (112) and carries out liquid-contacting to an outer surface of the reaction tube. A steam pipe (114) introduces the water steam for a heating which immersed into the thermal-medium oil and is manufactured with water-steam production and use plant, and heats the thermal-medium oil.    USE - For producing hydrogen useful as heat source of a hydrogen-production plant (102, 105).    ADVANTAGE - The hydrogen-production apparatus provides an improvement and installation simplification of energy utilization efficiency by diverting some water steam, e.g. an existing power generating plant, and setting it as the heat source of a hydrogen-production plant.    DETAILED DESCRIPTION - Hydrogen-production apparatus comprises fuel gas and raw material supply system (104) for supplying mixing steam containing a raw-water steam. A hydrogen-production apparatus has a modifier which heats and carries out the steam reforming of the mixing steam introduced from the raw material supply system with the water steam for a heating manufactured with a water-steam production and use plant (101), and produces hydrogen. The modifiers are several reaction tubes, which introduce the mixing steam. The catalyst is provided within the reaction, carries out the steam reforming of the mixing steam, and promotes a hydrogen production. A shell includes the reaction tube. Thermal-medium oil (113) retains in the shell and carries out liquid-contacting to the outer surface of the reaction tube. The steam pipe introduces the water steam for a heating which immersed into the thermal-medium oil and is manufactured with the water-steam production and use plant, and heats the thermal-medium oil. An INDEPENDENT CLAIM is included for a hydrogen-production method utilizing the above apparatus.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram showing the schematic structure of the hydrogen-production apparatus.    Water-steam production and use plant (101)    Hydrogen-production plant (102, 105)    Modifiers (103)    Raw material supply system (104)    Reaction tubes (111)    Shell (112)    Thermal-medium oil (113)    Steam pipe (114)    Catalyst (115)