NOVELTY - Operation of a fuel reformer involves vaporizing a mixture of water (2) and liquid hydrocarbon (1) using heating gas and introducing into a modification catalyst layer. A gaseous oxidizing agent, which is an oxygen-rich gas whose oxygen component ratio is larger than air, is used for partial oxidation modification reaction.    USE - For producing hydrogen-rich reformed gas. The fuel reformer is used as a heating gas supply apparatus, e.g. a fuel cell power generating device or a chemical processing plant.    ADVANTAGE - The method provides a high concentration of hydrogen in fuel reformed gas, reduces the loss of reaction heat and prevents the formation of ammonia.    DETAILED DESCRIPTION - Operation of a fuel reformer involves vaporizing a mixture of water and liquid hydrocarbon such as methane, methanol, ethanol and gasoline using heating gas. The vapor is passed through a modification catalyst layer with a gaseous oxidizing agent. A water vapor modification reaction and partial oxidation modification reaction are carried out simultaneously to form a hydrogen-rich reformed gas. The oxidizing agent for partial oxidation modification reaction is an oxygen-rich gas whose oxygen component ratio is larger than air.    An INDEPENDENT CLAIM is also included for a fuel reformer. A hydrocarbon system field heating gas is introduced to a modification catalyst layer. The fuel reformer comprises a modifier (5) for forming the hydrogen-rich reform gas, a heating gas supplying system (51) for supplying field heating gas to the modifier and an oxidizing region gas supply system (60) for supplying oxidizing gas to the modifier for both water vapor modification reaction and partial oxidization modification reaction. The oxidizing agent gas supply system has an oxygen and nitrogen separator (15) for a separation of oxygen and nitrogen, and an eliminator for removing nitrogen.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the fuel reformer. (Drawing includes non-English language text).    Liquid hydrocarbon (1)    Water (2)    Modifier (5)    Oxygen nitrogen separator (15)    Field heating gas supply system (51)    Oxygen gas supply system (60)