NOVELTY - Reforming apparatus (10) comprises selective oxidation unit (16) for reducing carbon monoxide in reformed gas that has passed through shift reactor (14). A reforming reaction tube (18) houses linearly reformer, the shift reactor and the selective oxidation unit. An outer casing (22) is disposed around the reforming reaction tube, and has a larger diameter than that of the reforming reaction tube. A heated flow passage (32) through which combustion exhaust gas passes to heat the reforming reaction tube is formed between the reforming reaction tube and the outer casing.    USE - Reforming apparatus, for use in a fuel cell, for reforming a raw fuel into a hydrogen-rich reformed gas.    ADVANTAGE - The reforming apparatus has a simplified structure with a desulfurizer. It has improved thermal efficiency and can be manufactured easily.    DETAILED DESCRIPTION - Reforming apparatus (10) comprises a reformer (12) for generating reformed gas from a raw fuel. A shift reactor (14) reduces carbon monoxide contained in the reformed gas through a shift reaction. A selective oxidation unit (16) reduces the carbon monoxide contained in the reformed gas that has passed through the shift reactor by performing selective oxidation on the carbon monoxide. A reforming reaction tube (18) houses linearly the reformer, the shift reactor and the selective oxidation unit. A combustion mechanism produces combustion exhaust gas by combusting the raw fuel. An outer casing (22) is disposed around the reforming reaction tube, and has a larger diameter than that of the reforming reaction tube. A heated flow passage (32) through which the combustion exhaust gas passes to heat the reforming reaction tube is formed between the reforming reaction tube and the outer casing. The apparatus has a desulfurizer which removes a sulfur component from the raw fuel and is housed in the reforming reaction tube.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional view illustrating the reforming apparatus for use in a fuel cell.    Reforming apparatus (10)    Reformer (12)    Shift reactor (14)    Selective oxidation unit (16)    Reforming reaction tube (18)    Outer casing (22)    Heated flow passage (32)