Separation membrane element

The present invention addresses the problem of providing a separation membrane element capable of stabilizing the separation/removal performance during operation of the separation membrane element. This separation membrane element is provided with at least a water collecting pipe, a separation membrane, a supply-side flow path member, and a permeation-side flow path member, and is characterized in that the supply-side flow path member is configured from a fibrous row X comprising a plurality of fibrous materials A arranged in one direction, and a fibrous row Y comprising a plurality of fibrous materials A arranged in the other direction; the fibrous row Y is composed of a plurality of fibrous objects B arranged in a different direction from the fibrous row X, the fibrous objects A and the fibrous objects B intersect to form intersection points, and the fibrous objects A and/or the fibrous objects B have a small diameter portion and a large diameter portion between adjacent intersection points in a cross secti