A device for protecting a product injection apparatus, particularly a syringe, said apparatus comprising a reservoir provided with a needle at its distal end and a piston connected to an actuator rod surmounted by a piston head, said device comprising: - a support sheath comprising a body able to receive the injection apparatus and a proximal end portion, - a protective sheath likely to slide with respect to the support sheath between a retracted standby configuration in which the needle is exposed and an extended protection configuration in which it covers the needle - first means (8, 10, 12, 13) for retaining the protective sheath in its standby configuration in a first position, called injection position, - second means (8, 14-17) for retaining the protective sheath in its standby configuration in a second position, called end-of-injection position, substantially offset in the distal direction, with respect to the support sheath, - an intermediate ring located in the proximal end portion of the support sheath, likely to slide with respect to this support sheath within said proximal end portion, said ring comprising means for cooperation with the piston head of the injection apparatus, and means for deactivating said first and second retaining means (8, 10, 12-17), - said first retaining means (8, 10, 12, 13) being likely to be deactivated by said means for deactivating said intermediate ring, by pressing the piston head in the distal direction on said cooperation means of said intermediate ring, for sliding the protective sheath, in its retracted standby configuration, between said first injection position and said second end-of-injection position, - and said second retaining means (8, 14-17) being likely to be deactivated by the means for deactivating said intermediate ring, by releasing the pressure of the piston head on said cooperation means of said intermediate ring, in order to allow the exit of the protective sheath under the action of pushing means, - characterized in that the deactivation means comprise a surface radially protruding from the body of the ring, this surface being able to cooperate with first tabs of the first retaining means and with second tabs of the second retaining means in order to deflect said first tabs and said second tabs circumferentially. - a support sheath comprising a body able to receive the injection apparatus and a proximal end portion, - a protective sheath likely to slide with respect to the support sheath between a retracted standby configuration in which the needle is exposed and an extended protection configuration in which it covers the needle - first means (8, 10, 12, 13) for retaining the protective sheath in its standby configuration in a first position, called injection position, - second means (8, 14-17) for retaining the protective sheath in its standby configuration in a second position, called end-of-injection position, substantially offset in the distal direction, with respect to the support sheath, - an intermediate ring located in the proximal end portion of the support sheath, likely to slide with respect to this support sheath within said proximal end portion, said ring comprising means for cooperation with the piston head of the injection apparatus, and means for deactivating said first and second retaining means (8, 10, 12-17), - said first retaining means (8, 10, 12, 13) being likely to be deactivated by said means for deactivating said intermediate ring, by pressing the piston head in the distal direction on said cooperation means of said intermediate ring, for sliding the protective sheath, in its retracted standby configuration, between said first injection position and said second end-of-injection position, - and said second retaining means (8, 14-17) being likely to be deactivated by the means for deactivating said intermediate ring, by releasing the pressure of the piston head on said cooperation means of said intermediate ring, in order to allow the exit of the protective sheath under the action of pushing means, - characterized in that the deactivation means comprise a surface radially protruding from the body of the ring, this surface being able to cooperate with first tabs of the first retaining means and with second tabs of the second retaining means in order to deflect said first tabs and said second tabs circumferentially.