The invention relates to a needle protection device (2) for a pre-filled syringe with staked needle. This device comprises a blocking mechanism (10), comprising means for fastening to a syringe body, a needle guard (20), into which the needle can be driven, and an after-use safety system (30, 40) comprising a sheath (40) defining a central axis along which it is movable, and a means (30) for elastically loading the sheath in a forward position in which it is able to cover the needle. The sheath comprises an outer tube and a coaxial inner tube which are manufactured in one piece by injection moulding, while the outer tube is configured in such a way as to cooperate with the blocking mechanism (10), and the inner tube is detachable from the outer tube and axially connected in translation to the needle guard (20).