NOVELTY - The cylindrical reformer has a combustion reaction unit and a fuel-converting catalytic reaction unit. Both the reaction units are structured as six cylindrical pipes for optimal heat exchange efficiency. The combustion reaction unit includes combustion portion, combustion gas distributor (15) and combustion gas passages (20,21).    USE - For use in production of hydrogen from fossil fuels for small fuel cell power plant.    ADVANTAGE - The compact cylindrical reformer is lightweight, minimizes heat loss and optimizes heat exchange efficiency. The reformer has favorable durability. The power efficiency of the fuel cell power system is improved by using the reformer. Since the reformer is lightweight, it is promptly operated according to initial start-up time or operation capacity change.    DETAILED DESCRIPTION - The cylindrical reformer has a combustion reaction unit and a fuel-converting catalytic reaction unit. Both the reaction units are structured as six cylindrical pipes for optimal heat exchange efficiency. The combustion reaction unit includes combustion portion, combustion gas distributor and combustion gas passages. The combustion portion burns air and fuel separated from air/fuel inlet (1). The distributor distributes the gas generated in combustion portion. The combustion gas passages guide the distributed combustion gas into discharge outlet (2). The catalytic reaction unit includes reforming reactors (36) for forming reforming reaction reformate, and water gas shift reactor (39) for forming water gas shift reformate provided between the reforming reactors to decrease concentration of carbon monoxide in reforming reaction reformate. The reforming reactors have catalyst for reforming feed and water supplied from feed/water inlet (3). The reforming catalyst of the reforming reactor, is nickel-based steam reforming catalyst or nickel-based steam reforming catalyst containing platinum or ruthenium. The water gas shift catalyst of water gas shift reactor is iron-chromium-based high-temperature shift catalyst, copper-zinc-based low-temperature shift catalyst or catalyst containing platinum or palladium. The pipe of reformer is made of aluminum alloy or ceramic material.    DESCRIPTION OF DRAWING(S) - The figure shows the longitudinal sectional view of internal structure of small cylindrical reformer.    air/fuel inlet (1)    discharge outlet (2)    feed/water inlet (3)    combustion gas distributor (15)    combustion gas passages (20,21)    reforming reactors (36)    water gas shift reactor (39)