Abstract: Provided is a three-dimensional flat cocoon product which is lightweight, has a favorable design and yields a highly uniform flat cocoon throughout the entire area thereof. The method of producing a flat cocoon product includes: expanding an expandable/contractible three-dimensional molding die; molding a flat cocoon by causing silkworms to crawl on an outer surface of the three-dimensional molding die and spin a cocoon; and contracting the three-dimensional molding die after the molding of the flat cocoon and extracting the contracted three-dimensional molding die from the flat cocoon.