A device for the back-injection of an implant including a holder to allow a user to hold the device, an injection needle, a retainer for retaining the implant before the injection needle, a plunger having a distal part for injecting the implant during withdrawal of the needle, a protective sleeve, capable of adopting an injection position leaving the needle uncovered and a safety position covering the needle again after use of the device, and a spring designed to move the protective sleeve into their safety position, the movement of the spring being controllable by the user.