the invention offers a microporous modified - polytetrafluoroethylene membrane that is a microporous membrane having a significantly small pore diameter and narrow pore - diameter distribution and that can remove microscopic foreign particles at high efficiency when used as a filtration membrane . a microporous modified - polytetrafluoroethylene membrane that is a microporous membrane produced by the steps of producing a copolymer of hexafluoropropylene or perfluoroalkyl ether and tetrafluoroethylene having the number of moles not less than 50 times that of the hexafluoropropylene or perfluoroalkyl ether , forming the copolymer into the shape of a membrane , heating the membrane to the melting point of the copolymer or above to bake the copolymer , cooling the obtained baked product , and stretching the baked product and that has a mean flow pore diameter of 30 nm or less ; a porous - modified - polytetrafluoroethylene - membrane composite that incorporates the microporous membrane and a production process of the composite ; and a separation membrane element incorporating the porous - modified - polytetrafluoroethylene - membrane composite .