NOVELTY - A reformer comprises a reforming part (1) for forming hydrogen-enriched reformed gas which performs water vapor modification of original fuel and water component, a selective oxidation part (3), a regulator for adjusting the temperature of oxidation reaction in the selective oxidation part using saturated water (vapor) and an inlet (9) for introducing saturated water (vapor) into the reforming part for water vapor modification.    USE - As a reformer.    ADVANTAGE - The temperature of the oxidation reaction in the selective oxidation part is controlled easily by a regulator using saturated water (vapor). The saturated water (vapor) is passed into the selective oxidation part as water component for water vapor modification, thereby generation of heat in the water vapor modification reaction is reduced. The reformer has favorable thermal efficiency, hence ejection of heat energy to the external atmosphere is reduced. The heat energy of the reformed gas or combustion gas is utilized efficiently.    DETAILED DESCRIPTION - A reformer comprises a reforming part (1) for forming hydrogen-enriched reformed gas which performs water vapor modification reaction of original fuel and water component, a shift reaction part (2) for reducing carbon monoxide contained in the reformed gas by an aqueous shift reaction, a selective oxidation part (3) and a combustion part (4). The selective oxidation part oxidizes selectively carbon monoxide in reformed gas obtained from the shift reaction part. The combustion part supplies combustion gas for forming heat energy in the reforming part. The reformer further has a regulator for adjusting temperature of oxidation reaction in the selective oxidation part using saturated water (vapor), and an inlet for introducing saturated water vapor into the reforming part as water component for water vapor modification.    DESCRIPTION OF DRAWING(S) - The figure shows an outline of the reformer. (Drawing includes non-English language text).    Reforming part (1)    Shift reaction part (2)    Selective oxidation part (3)    Combustion part (4)    Introduction unit (9)