A device for protecting a needle, provided to be mounted on a nose of a body of a cemented needle syringe, this device comprising: - an outer sleeve, which is movable along a longitudinal axis between a forward position, where it covers the needle, and a withdrawn position, where it does not cover the needle, - return means for returning the sleeve to the forward position, and - means for locking the sleeve in the forward position at the end of an injection characterized in that: - the device further includes a rigid needle shield including a flexible end-piece enclosed in a rigid sheath, this sheath comprising a first part and a second part, which is detachable from the first part by a rotational movement relative to the first part, the first part of the sheath comprising fastening means around the nose of the syringe, which allow solidarization in rotation of the first part of the sheath with the body of the syringe, - the two parts (16a, 16b) of the sheath are connected to one another by sectile bridges, designed to be broken when relative torque is applied between the two parts of the sheath, - the second part of the sheath protrudes out of the sleeve, so that it can be turned by a user and detached from the first part, the outer surface of the end-piece and the inner surface of the sheath being separated by a play, so that the end-piece does not risk rotating jointly with the front part 16a of the sheath 16 by friction, and - the device further includes means (140, 164) for translatable connection between the end-piece and the second part of the sheath, configured such that the end-piece and the second part of the sheath can be removed jointly from the syringe without rotating the end-piece around the needle. - an outer sleeve, which is movable along a longitudinal axis between a forward position, where it covers the needle, and a withdrawn position, where it does not cover the needle, - return means for returning the sleeve to the forward position, and - means for locking the sleeve in the forward position at the end of an injection - the device further includes a rigid needle shield including a flexible end-piece enclosed in a rigid sheath, this sheath comprising a first part and a second part, which is detachable from the first part by a rotational movement relative to the first part, the first part of the sheath comprising fastening means around the nose of the syringe, which allow solidarization in rotation of the first part of the sheath with the body of the syringe, - the two parts (16a, 16b) of the sheath are connected to one another by sectile bridges, designed to be broken when relative torque is applied between the two parts of the sheath, - the second part of the sheath protrudes out of the sleeve, so that it can be turned by a user and detached from the first part, the outer surface of the end-piece and the inner surface of the sheath being separated by a play, so that the end-piece does not risk rotating jointly with the front part 16a of the sheath 16 by friction, and - the device further includes means (140, 164) for translatable connection between the end-piece and the second part of the sheath, configured such that the end-piece and the second part of the sheath can be removed jointly from the syringe without rotating the end-piece around the needle.