NOVELTY - The reformer (30) for a fuel cell system to produce electrical energy using a hydrocarbon-based fuel, comprises a heating source (35) having an oxidizing catalyst for generating heat by a reaction of a fuel and an oxidant, and a reforming reaction part for generating hydrogen by a reforming catalyst reaction. The oxidizing catalyst comprises a solid acid comprised of an inorganic oxide and a strong acid ion bound to the inorganic oxide, a platinum-based metal supported on the solid acid, and a carrier supporting the solid acid and the platinum-based metal.    USE - The reformer is useful for a fuel cell system to produce electrical energy using a hydrocarbon-based fuel, and is useful for generating hydrogen from a fuel using a chemical catalyst reaction in which the hydrogen is supplied to the electricity generating element, where the cell is useful in portable electrical power sources for automobiles, distributed power sources for houses and public buildings and small electrical power sources for electronic devices.    ADVANTAGE - The reformer is capable of starting the fuel oxidation catalyst reaction at low temperature with heating source having a simplified structure.    DETAILED DESCRIPTION - The reformer (30) for a fuel cell system to produce electrical energy using a hydrocarbon-based fuel, comprises a heating source (35) having an oxidizing catalyst for generating heat by a reaction of a fuel and an oxidant, and a reforming reaction part for generating hydrogen by a reforming catalyst reaction. The oxidizing catalyst comprises a solid acid comprised of an inorganic oxide and a strong acid ion bound to the inorganic oxide, a platinum-based metal supported on the solid acid, and a carrier supporting the solid acid and the platinum-based metal. The heating source comprises a first and second reacting region including a platinum-based- and a non-platinum-based catalyst respectively in a volume ratio of 1:1 to 1:5. An INDEPENDENT CLAIM is included for a full cell system.    DESCRIPTION OF DRAWING(S) - The diagram shows a structure of a fuel cell system.    Stack (10)    Reformer (30)    Heating source (35)    Fuel supplier (50)    Oxidant supplier. (70)