A mixture of a fuel gas obtained by vaporizing hydrocarbon and air is burned in an engine 11 to generate mechanical power. The fuel gas obtained by reforming the hydrocarbon is supplied to a fuel electrode layer of a fuel cell module 13 in which plural electric power generating cells each including a solid electrolyte layer, and a fuel electrode layer and an air electrode layer disposed on both sides thereof are laminated, and the air or oxygen is supplied to the air electrode layer, so that the fuel cell module 13 is constructed to be capable of generating electric power at 930.degree. C. or lower. One of or both of mechanical power generated by the engine 11 and electric power generated by the fuel cell module 13 are outputted. As a raw material of the fuel gas supplied to the fuel cell module, gasoline, light oil or the like which can be supplied in a normal gasoline station can be used.