the surplus heat generated in the molten carbonate fuel cell bodies 11a and 11b is supplied through the heat exchanger 13 to the fuel treating devices 9a and 9b as the heat of reaction it is possible to supply the surplus heat directly to the fuel treating device for example by disposing the fuel treating device thermally adjacent to the fuel cell body also by holding the protective material for the electrolyte in the fuel treating devices 9a and 9b or in the molten carbonate fuel cell bodies 11a and 11b it is possible to assemble the electrolyte removing bed 16 into the fuel treating devices 9a and 9b or into the fuel cell bodies 11a and 11b besides for effective utilization of the steam produced in the fuel cell body for the reforming reaction in the fuel treating device a system has been studied in which a portion of the steam rich fuel gas discharged from the fuel cell body is recycled to the fuel treating device located on the upstream side of the fuel cell body in the system also the protective material 15 for the electrolyte according to the present invention can be used to prevent the lowering in the activity of the reforming catalyst due to the adhesion thereto of the electrolyte as has been described above it is apparent that the protective material for an electrolyte used in a.