NOVELTY - A reformer (100) comprises a heat source (160), a preheating portion (110) preheated by heat from the heat source, a pipe shaped reforming reaction unit (120) with internal surface having a rugged portion (150) which is heated by heat source, and a carbon monoxide processing unit (130) extending from the reforming reaction unit. The carbon monoxide processing unit extends in a pipe shape from reforming reaction unit and includes a shift reaction unit and carbon monoxide oxidation unit. The rugged portion further extends to internal surface of the carbon monoxide processing unit.    USE - For a fuel cell (claimed), and for generating reformed gas containing hydrogen from a fuel including butane. The fuel cell includes phosphoric acid fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, a polymer electrolyte fuel cell and alkaline fuel cell useful for power generation system.    ADVANTAGE - The reformer is rapidly preheated; and temperature of each reaction zone is easily controlled. By using the rugged portion and extended pipe design, the area heated by the heat source is increased and more heat is recovered, thereby improving thermal efficiency. The reformer reduces the carbon monoxide content of the reformed gas to the desired concentration by using two carbon monoxide processing units, installed integrally with the reformer portion, thus providing a miniaturized reformer suitable for a steam-reforming a fuel such as butane. The reformer prevents adverse effects such as coking of the catalyst layer in each reaction zone, and properly maintains the ratio of steam to carbon while properly maintaining the optimum reaction temperature thus maintaining catalyst efficiency.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the reformer.    reformer (100)    preheating portion (110)    pipe (112)    reforming reaction unit (120)    catalyst layer (124)    carbon monoxide processing unit (130)    rugged portion (150)    heat source (160)