NOVELTY - The fuel reformer system (20) comprises modifier (22), carbon-monoxide selective-oxidation apparatus (30), cooling system (40), reaction tank and start-up-control unit. The modifier generates hydrogen rich gas, and the carbon monoxide selective-oxidation apparatus oxidizes carbon monoxide in the hydrogen rich gas generated by modifier. The carbon-monoxide selective-oxidation apparatus has several cooling system, and the start-up control unit controls the gas-cooling unit not to cool hydrogen rich gas from the modifier at the time of start-up of the fuel reformer system.    USE - Fuel reformer system.    ADVANTAGE - The fuel reformer system is effective in operation and effectively prevents dangerous effects. At time of start-up, sufficient quantity of water-vapor is generated, and temperature of oxidation apparatus is sufficiently controllable.    DETAILED DESCRIPTION - The fuel reformer system comprises modifier, carbon-monoxide selective-oxidation apparatus, cooling system, reaction tank, steam supply unit, gas-cooling system and start-up-control unit. The modifier generates hydrogen rich gas for fuel of hydrocarbon type by steam reforming process, and the carbon monoxide selective-oxidation apparatus oxidizes carbon monoxide in the hydrogen rich gas generated by modifier. The carbon-monoxide selective-oxidation apparatus has several cooling system which cools reaction tank performing oxidation with catalyst. At the time of start-up of carbon-monoxide selective oxidation apparatus, the reaction tank is cooled by cooling system (A), and which the cooling system is controlled by cooling-control unit and use water as cooling medium. The water in the cooling system is generated as water vapor, and the water-vapor supply unit supplies generated water-vapor to modifier. The water-vapor supply unit is positioned between modifier and carbon-monoxide selective-oxidation apparatus, and gas-cooling unit cools the hydrogen-rich gas from the modifier. The start-up control unit controls the gas-cooling unit not to cool hydrogen rich gas from the modifier at the time of start-up of the fuel reformer system. An INDEPENDENT CLAIM is included for the combine system of carbon monoxide selective oxidation apparatus and water-vapor generation apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows the block diagram of the structure of fuel reformer system. (Drawing includes non-English language text)    Fuel reformer system (20)    Modifier (22)    Heating portion (24)    Modification portion (26)    Heat exchanger (28)    Carbon monoxide selective-oxidation apparatus (30)    Cooling system-A (40)    Water-vapor generator (60)    Electronic control unit (80)