The invention reduces drug leakage in injection devices in which the syringe and needle hub are separable. The injection needle assembly (2) comprises a needle tube (5) having a needle point that pierces the skin, and a needle hub (6) having a first member (11) that holds the needle tube (5) and a second member (12) into which the dispensing part (52) of a syringe (3) is fitted. The assembly also comprises an elastic member (61) having: a main body (41) that is disposed inside the second member (12) and has a through hole into which the needle tube (5) is inserted and a protruding part (65) that is formed on the rim of the main body (41) on the side facing the dispensing part (52) of the syringe (3) and obtained from a thin-walled member that can deform towards the inner circumferential surface of the second member (12). The protruding part (65) of the elastic member (61) is pressed by the drug that is dispensed from the dispensing part (52) of the syringe (3) and contacts the inner circumferential surface of the second member (12) in a liquid-tight manner.La présente invention permet de réduire la fuite de médicament dans les dispositifs dinjection dans lesquels la seringue et le pavillon daiguille peuvent être séparés. Lensemble daiguille dinjection (2) comprend un tube daiguille (5) ayant une pointe daiguille qui perce la peau, et un pavillon daiguille (6) ayant un premier élément (11) qui tient le tube daiguille (5) et un second élément (12) dans lequel sadapte la partie de distribution (52) dune seringue (3). Lensemble comprend également un élément élastique (61) ayant : un corps principal (41) qui est disposé à lintérieur du second élément (12) et possède un trou débouchant dans lequel le tube daiguille (5) est inséré et une partie en saillie (65) qui est formée sur le bord du corps principal (41) sur le côté faisant face à la partie dadministration (52) de la seringue (3) et provenant dun élément à parois fines qui peut se déformer vers la surface circonfére
