NOVELTY - A reformer has modification reaction part (M) for forming reformed gas (G), and parts A,B for recovering heat from M and cooling G in M respectively. Shift reaction part (S) which reduces carbon monoxide (CO) amount in G, and recovery parts C,D for recovering heat from S and cooling G in S respectively are comprised. CO selective oxidation reaction part (O), and heat recovery parts E,F, are comprised.    USE - For forming hydrogen from hydrocarbon raw material gas, used for fuel cell and hydrogen engine.    ADVANTAGE - The compact reformer refines hydrocarbon raw material gas easily and efficiently. The reduction of heat release from reformer is enabled. The use of external heat supply for regular operation of the reformer, is eliminated. The heat generated during reduction process and oxidation treatment, is reduced. The catalyst for shift reaction part has high reactivity and high selectivity, and is maintained in medium temperature to low temperature region. An unit for conveying raw material gas or reformed gas is eliminated.    DETAILED DESCRIPTION - The reformer has modification reaction part which forms hydrogen rich reformed gas by partial oxidation of raw material gas, 1st heat recovery part which recovers reaction heat generated in the reaction part and 2nd heat recovery part which cools reformed gas formed in the modification reaction part, and recovers exhaust heat. A shift reaction part which reduces carbon monoxide concentration in reformed gas by water gas shift reaction, 3rd heat recovery part which recovers reaction heat generated by shift reaction part and 4th heat recovery part which cools reformed gas formed by shift reaction part, and recovers exhaust heat, are comprised. Carbon monoxide selective oxidation reaction part which reduces concentration of carbon monoxide in reformed gas and 5th heat recovery part which recovers reaction heat generated by carbon monoxide selective oxidation reaction part, and 6th heat recovery part which cools the reformed gas formed by carbon monoxide selective oxidation reaction part, and recovers the exhaust heat, are comprised. The reformed gas from modification reaction part and shift reaction part, flows to 2nd and 6th heat recovery parts through 4th heat recovery part and carbon monoxide selective oxidation reaction part. The modification reaction part, shift reaction part, and 2nd, 6th and 4th heat recovery parts are provided integrally.    DESCRIPTION OF DRAWING(S) - The figure shows the structure of fuel cell system equipped with reformer. (Drawing includes non-English language text).    Container (30)