NOVELTY - A modification catalyst is filled in a modification pipe (3). An intermediate pipe (21) is arranged in the outer surface of a linear inner pipe (20) and is formed in the shape of polygon or wave. A reformed-gas route (23) is formed between the inner and intermediate pipes. An outer pipe (22) is arranged in outer surface of intermediate pipe contacting each vertex of the intermediate pipe.    USE - For generating hydrogen used in fuel cells.    ADVANTAGE - Since the outer pipe contacts the vertex of the intermediate pipe, the heat of the waste gas is conducted efficiently and heating efficiency is enhanced. The need for a heat exchanger is eliminated, simplifying the structure of the hydrogen generator.    DETAILED DESCRIPTION - A fuel supply pipe (4) and a water supply unit supply fuel and water to the modification pipe, respectively. A combustion tube (6) is installed in the inner pipe to supply heat for modification reaction, by combustion of fuel. The fuel and water containing organic compound react in the space between the inner and intermediate pipes, generating hydrogen-rich gas. A heat insulation material (8) of specific size, insulates the outer pipe such that the surface temperature of the heat insulating material is regulated at 200-300 degrees C. A heat-transfer promotion material or a thermal storage material is arranged in the exit of a modifier. A selective oxidation catalyst (10) of a carbon monoxide removal device (11), treats carbon monoxide contained in the reformed gas. A carbon monoxide transformer (9) transforms carbon monoxide into carbon dioxide, by reacting with air or oxygen.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the hydrogen generator. (Drawing includes non-English language text).    modification pipe (3)    fuel supply pipe (4)    combustion tube (6)    heat insulation material (8)    carbon monoxide transformer (9)    selective oxidation catalyst (10)    carbon monoxide removal device (11)    inner pipe (20)    intermediate pipe (21)    outer pipe (22)    reformed-gas route (23)