NOVELTY - A reformer for obtaining a reformed gas from raw material gas, comprises vessel; fixed tube plate inside vessel and partitioning vessel to form a channel in an end portion of the vessel; floating head inside vessel on the other end portion; reaction tube containing reforming catalyst; raw material gas inlet; reformed gas outlet; heating gas inlet and heating gas outlet; and cooling mechanism for cooling fixed tube plate.    USE - For obtaining a reformed gas (synthesis gas) from raw material gas (natural gas).    ADVANTAGE - The reformer can restrain the occurrence of problems caused by thermal expansion and thermal stress without decreasing the methane conversion efficiency and heat transfer efficiency while having a structure suitable for larger size reformer. It is capable of using a wide range of gases as the high-temperature heat source for the reforming reaction.    DETAILED DESCRIPTION - A reformer for obtaining a reformed gas from raw material gas, comprises vessel (1); fixed tube plate (21) inside vessel and partitioning vessel to form a channel in an end portion of the vessel; floating head (31) inside vessel on the other end portion; reaction tube (11) containing reforming catalyst (12), one end of reaction tube being connected to the fixed tube plate in communication with channel and the other end being in communication with interior of floating head via a first flexible tube joint; raw material gas inlet (2) in communication with interior of floating head via a second flexible tube joint; reformed gas outlet (3) in communication with channel; heating gas inlet (4) and heating gas outlet (5) between the fixed tube plate and floating head, the heating gas inlet being closer to the fixed tube plate and the heating gas outlet being closer to the floating head; and cooling mechanism (23) for cooling fixed tube plate.    DESCRIPTION OF DRAWING(S) - The figure is a schematic sectional view of a reformer.    Vessel (1)    Raw material gas inlet (2)    Reformed gas outlet (3)    Heating gas inlet (4)    Heating gas outlet (5)    Reaction tube (11)    Reforming catalyst (12)    Fixed tube plate (21)    Cooling mechanism (23)    Floating head (31)