A manufacturing method for manufacturing a fuel cell separator assembly includes a joining step for bringing opposing projections of uneven portions of separators into contact with each other through use of pressing members to join the projections through use of a welding robot. In the joining step, an elastic member is interposed between the pressing members and at least one of first and second separators so that a pressing force from the pressing members is imparted to the first and second separators. In this way, the opposing projections are brought into contact with each other by elastic deformation of the elastic member.