NOVELTY - A fuel reformer (1) has modifier (24), catalyst temperature sensor (31), selective-oxidation air blower (30) and control unit. Modifier produces reformed gas by steam reforming of mineral fuel and hydrocarbon raw material. Sensor (31) detects temperature of carbon monoxide selective-oxidation catalyst used for selective-oxidation of carbon monoxide contained in reformer gas. Blower (30) supplies selective oxidation air to oxidation catalyst. Control unit controls output of air blower in direction increasing air flow amount based on preset temperature difference.    USE - Fuel reformer is used for modifying fuel gas supplied to anode of fuel cell.    ADVANTAGE - The fuel reformer has improved starting reliability and stable electric power generation property. The influence of carbon monoxide-group poisoning property of fuel reformer is reduced.    DETAILED DESCRIPTION - A fuel reformer (1) has a modifier (24), a catalyst temperature sensor (31), a selective-oxidation air blower (30) and a control unit. The modifier produces reformed gas by carrying out steam reforming of mineral fuel and hydrocarbon group raw material, such as natural gas and liquefied petroleum gas. The sensor (31) detects temperature of carbon monoxide selective-oxidation catalyst used for selective-oxidation of carbon monoxide contained in reformer gas in presence of oxygen in carbon monoxide selective oxidation reactor (26). The blower (30) supplies selective oxidation air to carbon monoxide selective oxidation catalyst. The control unit controls output of air blower in direction increasing air flow amount, when a temperature difference between predetermined setting catalyst temperature at the time of completion of electric power generation, and detected catalyst temperature exist.    DESCRIPTION OF DRAWING(S) - The drawing shows the block diagram of the control system of fuel reformer. (Drawing includes non-English language text)    Fuel reformer (1)    Desulfurizer (23)    Modifier (24)    Carbon monoxide selective oxidation reactor (26)    Selective-oxidation air blower (30)    Catalyst temperature sensor (31)