The separation membrane element

PROBLEM TO BE SOLVED: To provide a separation membrane element capable of increasing transmission fluid amount per unit time and improving stability performance.SOLUTION: A separation membrane element is constituted with a separation membrane which comprises a separation function layer arranged on a surface 1 and a nonwoven fabric as base material arranged on the back surface 2 and a permeation side channel material 3 arranged the back surface side of the base material. Therein, the permeation side channel material 3 is constituted with material different from the separation membrane, the separation membrane is a reverse osmosis membrane, the transmission side channel material 3 is impregnated with a thickness of 5 μm or more in the separation membrane, permeation side channel material is striped or dotted, has a width of 300 to 2000 μm and has a pitch of 0.8 to 5 mm and a projection area ratio of the permeation side channel material 3 with respect to the separation membrane is 0.03 to 0.80.