The present invention provides an attachment device for a separation film element in a separation film module. The attachment device facilitates a maintenance operation, has excellent durability under various usage conditions, and is cost effective. A sealing member of an attachment device for a separation film element (3) of a separation film module (1) comprises a plurality of segmented round packing elements (7) having, for example, a segmented rounded shape as viewed from a graphite plane surface. The plurality of segmented round packing elements (7) are stacked stepwise to fit onto and cover a top end (3a) of the separation film element (3), and cutout sections (8, 8) of vertically-adjacent segmented round packing elements (7a, 7b) are, when viewed from the plane surface, positioned at mutually different locations. The stepwise-stacked segmented round packing elements (7) are received by an inward-projecting annular receiving part (12) in a tube sheet attachment hole (11), and the stepwise-stacked segmented round packing elements (7) are then tightly pressed into the annular receiving part (12) by screwing in a pressing bracket (20), thus forming a tight seal.