NOVELTY - Fuel cell system (100) reformer (30) comprises reaction sections, where at least one of the reaction sections has a channel; cover plate; and bonding joint between two reaction sections and between the reaction sections and cover plate to couple the reaction sections and the cover plate to each other.    USE - For fuel cell system used in converting chemical reaction energy of oxygen and hydrogen contained in hydrocarbon material such as methanol, ethanol, or natural gas into electric energy.    ADVANTAGE - The inventive reformer is formed by stacking reaction plates having respective channels for enabling the flow of a fuel or a gas, thus the size of the reformer can be reduced and the fuel cell system is allowed to be compact.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (A) a method of manufacturing a reformer of a fuel cell system, comprising preparing reaction sections in which a channel is formed in reaction sections and cover plate; loading at least one metal film having an opening corresponding to the channel between the reaction sections and the cover plate; heating the reaction sections and the cover plate in a state when the reaction sections and the cover plate contact each other; and melting the metal film to braze the at least one of the reaction sections with the at least one cover plate; and    (B) a fuel cell system comprising a reformer for generating hydrogen from a fuel containing hydrogen, electricity generator for generating electric energy through an electrochemical reaction of hydrogen and oxygen, fuel supply unit for supplying the fuel to the reformer, and oxygen supply unit for supplying oxygen to the reformer and the at least one electricity generator.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of an entire construction of a fuel cell system.    Electricity generator (11)    Separator (16)    Reformer (30)    Fuel supply unit (50)    Oxygen supply unit (70)    Fuel cell system (100)