This device (1) comprising a body (2), a sleeve (3) mobile in relation to said body (2), and locking means (5, 6, 7) enabling locking of the sleeve (3) in a protective position； the sleeve (3) can be moved between a non-protective position, in which an injection member comprised by the injection apparatus is exposed, and said protective position； said locking means (5, 6, 7) comprise at least one flexible proximal leg (7). According to the invention, - the leg (7) comprises a tilted edge (7d) extending over its entire length, forming said additional bearing surface comprised by said leg (7), and -the device comprises at least one wall (10) having a tilted rectilinear edge (10c) also extending over the entire length of this wall, forming said additional bearing surface (10c) of the device (1).
