Device (1) for protecting an injection device, in particular an injection device for medical use, such as a syringe, including a body (2) in which the injection device is placed, a sleeve (3) movable in relation to said body (2), means (4) for moving said sleeve (3) in relation to body (2), and locking means (5, 6, 7) that make it possible to lock the sleeve (3) in a position of protection； the sleeve (3) can move between a non-protective position, in which an injection element composed of the injection apparatus is exposed in order to allow injection, and said protective position, in which the sleeve (3 ) completely covers the injection element； said locking means (5, 6, 7) include at least one flexible proximal leg (7) integral with the sleeve (3), forming a first support surface (7a) through which said leg (7) engages, in said protective position, behind at least one corresponding distal first supporting surface of said body (2)； the flexible proximal leg (7) has a reduced thickness, such that it can assume a position between a body of the injection apparatus and the body (2) of the device (1)； The leg (7) includes at least one additional support surface (7b, 7c) arranged above, and the device (1) includes at least one corresponding additional support surface (11b, 11c, 10c), these respective surfaces being capable of additional supports (7b, 7c； 11b, 11c, 10c) to abut one another when a force is exerted on the sleeve (3) in the direction that tends to make said sleeve (3) return towards said non-protective position； The leg (7) includes two additional support surfaces (7b, 7c), of which a first is arranged to retain the leg (7) along the longitudinal direction of said leg (7) and of which the second is arranged so as to retain the leg (7) in the circumferential direction, characterized in that said device (1) includes two corresponding additional supporting surfaces (11b, 11c). - the leg (7) has an enlarged upper portion, which forms an extension in the circumfe
