A MEA-frame assembly is arranged in a mold for injection molding to form a first flow passage arranged so as to extend along the outer periphery of an electrode between the outer periphery of the electrode and the inner periphery of a frame, a second flow passage arranged so as to extend along an inner elastic member between the inner periphery and outer periphery of the frame and a plurality of connecting flow passages which communicate the first flow passage with the second flow passage. An elastic resin is injected into the first flow passage to fill the first flow passage with the elastic resin and to fill the second flow passage with the elastic resin through each of the communicating flow passages, thereby an elastic member which hermetically seals the space between the MEA-frame assembly and the separator is integrally formed.