Separation membrane element

A separation membrane element comprising:

• a water collection tube;
• and a plurality of separation membrane leaves stacked on each other and wound around the water collection tube,
• wherein each of the separation membrane leaves comprises one or more separation membranes each having a feed-side face and a permeate-side face and is configured so that the feed-side faces face each other,
• a sheet having a plurality of projections fixed thereto is provided between the permeate-side faces of the separation membrane leaves stacked on each other, wherein the plurality of projections are impregnated into the sheet,
• regarding a height of the projections, a ratio of the maximum height to the minimum height of one projection in the cross section in a lengthwise direction of the separation membrane is from 1.10 to 1.50, and a variation coefficient of the height of the projections in one and the same plane is from 0.02 to 0.15, and
• an impregnation ratio of the projections into the sheet is from 10% to 100%.