Device for protecting an injection apparatus, in particular an injection apparatus for medical use such as a syringe, comprising a body in which the injection apparatus is placed, a sleeve mobile in relation to said body, means for moving this sleeve in relation to the body, and locking means (5, 6, 7) making it possible to lock the sleeve in a protective position; the sleeve can be moved between a non-protective position, in which an injection member comprised by the injection apparatus is exposed so as to allow injection, and said protective position, in which the sleeve completely covers the injection member; said locking means (5, 6, 7) comprise at least one flexible proximal leg integral with the sleeve, forming a first bearing surface through which said leg engages, in said protective position, behind at least a first corresponding distal bearing surface arranged of said body; the flexible proximal leg has a reduced thickness, such that it can assume a position between a body of the injection apparatus and the body of the device; the leg comprises at least one additional bearing surface (7b, 7c) arranged thereon, and in that the device comprises at least one corresponding additional bearing surface (11 b, 11c, 10c), these respective additional bearing surfaces (7b, 7c; 11 b, 11c, 10c) being able to bear against each other when a force is exerted on the sleeve in the direction tending to return this sleeve toward said non-protective position. the leg comprises two additional bearing surfaces (7b, 7c), a first of which is arranged so as to constrain the leg along the longitudinal direction of said leg and the second of which is arranged so as to constrain the leg in the circumferential direction, characterized in that said device comprising two corresponding additional bearing surfaces (11b, 11c). - the leg has an enlarged upper portion, forming an extension in the circumferential direction, this extension having a lower edge which forms said first additional bearing surface and an end edge in the circumferential direction, which forms said second additional bearing surface, and - the sleeve comprises at least one proximal wall located in the vicinity of the leg, presenting a notch forming a first rim, extending substantially in the transverse direction relative to the axis of sliding of the sleeve, able to cooperate with said first additional bearing surface of the leg, and a second rim, extending substantially in the longitudinal direction relative to the axis of sliding of the sleeve, able to cooperate with said second additional bearing surface of the leg. - the leg has an enlarged upper portion, forming an extension in the circumferential direction, this extension having a lower edge which forms said first additional bearing surface and an end edge in the circumferential direction, which forms said second additional bearing surface, and - the sleeve comprises at least one proximal wall located in the vicinity of the leg, presenting a notch forming a first rim, extending substantially in the transverse direction relative to the axis of sliding of the sleeve, able to cooperate with said first additional bearing surface of the leg, and a second rim, extending substantially in the longitudinal direction relative to the axis of sliding of the sleeve, able to cooperate with said second additional bearing surface of the leg.