NOVELTY - A hydrogen generator has main component (50) comprising reforming-raw material flow path (1), reforming portion (10), reformed-gas flow path (2), carbon monoxide (CO) modifying portion (15) and modified gas flow path (3). The flow path (1) supplies raw material to portion (10). The flow path (2) supplies reformed gas to portion (15). The flow paths (1,3) are positioned such that heat transfers between flow paths (3 and 1).    USE - For generating fuel gas having hydrogen as main constituent used for fuel cell electric power generating system (claimed).    ADVANTAGE - The hydrogen generator has improved thermal efficiency, as heat of modified gas and radiant heat are effectively transferred to to-be-reformed raw material.    DETAILED DESCRIPTION - A hydrogen generator has a main structural component (50) comprising reforming-raw material flow path (1), reforming portion (10), reformed-gas flow path (2), carbon monoxide (CO) modifying portion (15) and modified gas flow path (3). The flow path (1) supplies to-be-reformed raw material to the reforming portion. The reforming portion generates reformed gas consisting mainly of hydrogen, by reforming the raw material. The flow path (2) supplies reformed gas from the reforming portion to the CO modifying portion. The CO modifying portion converts CO contained in the reformed gas to carbon dioxide. The flow path (3) passes modified gas from the CO modifying portion. The flow path (3) is positioned adjacent to flow path (1) so that heat transfers from flow path (3) to flow path (1).    To-be-reformed raw material contains hydrocarbon-type source gas and water as vapor. CO modifying portion consists of modifying catalyst. The modifying catalyst consists of platinum group metal supported on metal oxide containing at least aluminum, and cerium and zirconium.    An INDEPENDENT CLAIM is included for fuel cell electric power generating system.    DESCRIPTION OF DRAWING(S) - The figure shows sectional view of structure of the hydrogen generator.    Reforming-raw material flow path (1)    Reformed-gas flow path (2)    Modified gas flow path (3)    Reforming portion (10)    Carbon monoxide modifying portion (15)    Main structural component (50)