NOVELTY - A fuel processing device for a fuel cell system, has a first reformer that generates hydrogen through an electrolysis reaction of a hydrogen-containing fuel using electrical energy; and a second reformer that generates hydrogen through a reformation reaction of the fuel using thermal energy. It is connected to a stack that generates electricity through a reaction between hydrogen and oxygen. It provides the stack with hydrogen.    USE - For a fuel cell system (claimed).    ADVANTAGE - The inventive device generates hydrogen from fuel using the electric energy and the thermal energy. It shortens the starting-up time of the fuel cell system, and distributes the load that is concentrated on the reformer using the heat. It further enhances the performance of the whole fuel cell system. It reduces the amount of fuel consumption and improves the thermal efficiency of the whole fuel cell system.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a fuel cell system, comprising a stack (10) that generates electrical energy through a reaction between hydrogen and oxygen; a fuel processing device (30) that is connected to the stack to generate hydrogen from fuel and that supplies the hydrogen to the stack; a fuel supply unit (50) that supplies the fuel to the fuel processing device; and an air supply unit (70) that supplies air to the stack and the fuel processing unit, where the fuel processing device comprises the first reformer (20) that generates byproducts along with the hydrogen through the electrolysis reaction of the fuel using electrical energy and the second reformer (40) that generates hydrogen through the reformation reaction of the fuel using the thermal energy; and    (2) a method of driving a fuel cell system that comprises the stack, comprising supplying fuel to a first reformer and a second reformer to start up the fuel cell system; allowing the first reformer to generate the hydrogen and to supply the generated hydrogen to the stack; and allowing the second reformer to generate the hydrogen and to supply the generated hydrogen to the stack.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram that schematically illustrates an entire construction of a fuel cell system.    Stack (10)    First reformer (20)    Fuel processing device (30)    Second reformer (40)    Fuel supply unit (50)    Fuel tank (51)    Air supply unit (70)