| abstract |
A separation membrane element which is equipped with a perforated water collection tube and an envelope-shaped membrane which is constituted of a separation membrane and has been wound around the periphery of the perforated water collection tube, wherein at least one surface of the separation membrane has a difference in surface level of 100-2,000 µm and the separation membrane has a band-shaped region having an average difference in surface level of 50 µm or less, in each of both ends thereof with respect to the longitudinal direction of the perforated water collection tube. |