[Claim 1]
A separation membrane element comprising at least a water collection tube, a separation membrane, a feed-side channel material, and a permeate-side channel material, wherein
the feed-side channel material is configured of a fibrous row X configured of a plurality of fiber-form objects A arranged in one direction and a fibrous row Y configured of a plurality of fiber-form objects B arranged in a direction different from the direction for the fibrous row X,
the fiber-form objects A intersect the fiber-form objects B to form intersections, and
the fiber-form objects A and/or the fiber-form objects B have a small-diameter part and a large-diameter part between adjacent intersections in a section thereof parallel to the respective fibrous row.
[Claim 2]
The separation membrane element according to claim 1, wherein the feed-side channel material has a proportion of a length of the small-diameter part to an interval between the intersections being 0.25 or more and 0.80 or less.
[Claim 3]
The separation membrane element according to claim 1 or 2, wherein a proportion of an average diameter of the small-diameter part to an average diameter of the large-diameter part is 0.17 or more and 0.78 or less.
[Claim 4]
A separation membrane element comprising at least a water collection tube, a separation membrane, a feed-side channel material, and a permeate-side channel material, wherein
the feed-side channel material has regions therein which have been separated by fiber-form objects and are reticulately continuous,
the regions are each defined by four approximate curves, two approximate curves of which form an approximate parabola,
in cases when a straight line connecting both ends of the approximate parabola is

referred to as a straight line L, and when
an area of a portion surrounded by the straight line L and the approximate parabola is expressed by S1, and an area of a portion in the region other than S1 is expressed by S2, then
the S1 and the S2 satisfy the relationship S1>S2, and
the fiber-form objects have a large-diameter part having a diameter R1 and a small-diameter part having a diameter R2, the R1 and the R2 satisfying the relationship R1>R2.
[Claim 5]
The separation membrane element according to claim 4, wherein a proportion of a length of the small-diameter part to a length of the approximate parabola connecting intersections in the feed-side channel material is 0.25 or more and 0.80 or less.
[Claim 6]
The separation membrane element according to any one of claims 1 to 5, wherein the small-diameter part has been disposed in a middle position with respect to the large-diameter part in the thickness direction of the feed-side channel material.
[Claim 7]
The separation membrane element according to any one of claims 4 to 6, wherein a proportion of the diameter R2 of the small-diameter part to the diameter R1 of the large-diameter part is 0.17 or more and 0.78 or less.
[Claim 8]
The separation membrane element according to any one of claims 1 to 7, wherein the small-diameter part has a tensile modulus of 200 MPa or more and 1,000 MPa or less.
[Claim 9]
The separation membrane element according to any one of claims 1 to 8, wherein the large-diameter part has been disposed at one end of the small-diameter part.