A separation membrane module (1A) is provided with: a cylindrical pressure vessel (7); a plurality of separation membrane elements (2), which are inserted into the pressure vessel (7), and have a first end member (3) and a second end member (4); and a seal member (5A), which is attached to one of or both of the first end member (3) and the second end member (4), said members being adjacent to each other. The seal member (5A) is normally stored inside of the maximum diameter of the first end member (3) and/or the second end member (4), said first end member and/or the second end member having the seal member attached thereto, and the seal member is adhered to the inner circumferential surface (7a) of the pressure vessel (7) by being deformed by abutting of the adjacent separation membrane elements (2) on each other or supply of a pressurizing fluid to the inside of the pressure vessel (7).