NOVELTY - The reformer which produces hydrogen from reformed raw material gas has a modification-reaction portion (1) and a water gas shift portion (2). A reformed gas containing hydrogen is produced from the downstream side of the portion (1) by modification reaction of reformed raw material gas. Carbon monoxide present in the generated reformed gas is decreased by water gas shift reaction, in portion (2).    USE - For producing hydrogen used as fuel in fuel cell systems of fuel cell electric vehicles, from reformed raw material gas.    ADVANTAGE - The reformer is small, highly efficient and practical. The water gas shift portion of the reformer has a simple structure and reduced size. The concentration of carbon monoxide in the formed reformed gas is maintained below a predetermined value by the use of a shift catalyst. The produced reformed gas is cooled effectively without the use of forced cooling methods.    DETAILED DESCRIPTION - The reformer which produces hydrogen from reformed raw material gas has a modification-reaction portion (1) and a water gas shift portion (2). A reformed gas containing hydrogen is produced from the downstream side of the modification-reaction portion by modification reaction of reformed raw material gas. Carbon monoxide present in the generated reformed gas is decreased by water gas shift reaction, in the water gas shift portion. The water gas shift portion has a container center side gas passage way (23) and a peripheral-side gas passageway (25). The center side gas passageway divides the inside of cylindrical container (21). The water gas shift reaction of the reformed gas is carried out in the presence of a shift catalyst in the gas passageway provided in the cylindrical container. The inlet (22) of the reformed gas is connected to container center side gas passageway and the outlet (26) of the reformed gas is connected to the peripheral-side gas passageway.    DESCRIPTION OF DRAWING(S) - The figures show entire-schematic block diagram of a reformer, axial sectional view of a water gas shift portion and sectional view on A-A line of the water gas shift portion. (Drawing includes non-English language text).    modification-reaction portion (1)    water gas shift portion (2)    container (21)    gas inlet (22)    container center-side gas passageway (23)    peripheral-side gas passageway (25)    gas outlet. (26)