TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The reformed gas produced in reforming reaction region (I) and fluid containing oxygen-containing gas are supplied to secondary reforming reaction region (II), and contacted with secondary reforming catalyst (C2). The reforming reaction region is maintained at maximum temperature of 400-1200degreesC. The outlet temperature of region (II) is higher than that of region (I). A reformed gas containing hydrogen and carbon monoxide is produced. Water vapor and/or carbon dioxide-containing gas is further supplied to region (II). A hydrogen-containing gas is further supplied to reforming reaction region. The hydrogen-containing gas and oxygen-containing gas are supplied to reforming reaction region, and hydrogen is burned such that the temperature of the reaction region reaches desired operating temperature required for reforming. The fuel, water vapor and/or carbon dioxide-containing gas, and oxygen-containing gas are desulfurized before supplying to reforming reaction regions (I,II). The fluid (F) has sulfur compound concentration of less than 2.4 mol.ppb, before performing reforming reaction. Preferred Conditions: The thermal decomposition index temperature of fuel is value of lowest temperature of thermal decomposition temperature obtained based on concentration of hydrocarbon in fuel. The feed rate ratio of water vapor and/or carbon dioxide-containing gas, and oxygen containing gas is changed, and temperature of regions (I,II) is adjusted. The concentration of hydrocarbon is concentration measured at inlet port of reaction chamber. Preferred Property: The total flow rate of gas supplied to reforming reaction region is 750-300000 hour-1 with respect to gas space velocity per time. Preferred Fuel: The fuel is natural gas containing 50% or more of methane. Preferred Apparatus: The unit (A) is temperature sensor for detecting the temperature of reforming reaction region and a control unit for adjusting feed rate of water vapor and/or carbon dioxide-containing gas and oxygen-containing gas based on detected value. The reforming reaction region has a cooling or heating temperature control unit. The reforming gas manufacturing apparatus further has desulfurizing apparatus and reaction chamber for accommodating catalyst (C2).    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The reforming catalyst (C1,C2) contain metal having steam-reforming capability as main component.