The device comprises a syringe (10, 11, 12) and safety means comprising a protective sheath (16) capable of adopting, relative to the syringe body, both an injection configuration in which the syringe needle (11) projects beyond said sheath, and a protection configuration in which the needle extends inside the sheath. The device includes a trigger member (30) enabling it to pass from the injection configuration to the protection configuration at the end of the injection stroke. It comprises means (34) for defining a first end-of-injection-stroke situation in which the trigger member (30) is unsuitable for causing the device to pass from the injection configuration to the protection configuration, and a second end-of-injection-stroke situation in which such passage is possible.