Abstract: The syringe (S) comprises a body (K) forming a liquid reservoir, carrying a needle (A) for injecting the liquid, and having a plunger (P) movably mounted in the body (K). The body (K) is housed in a safety sheath (1) to be axially movable between an active position in which the needle (A) projects through a distal end of the sheath (1) and a protection position in which the needle (A) is retracted inside the sheath (1) and towards which position the body (K) is urged resiliently. The body (K) is prevented from moving relative to the sheath in the active position by locking means (6) that opposite the resilient force on the body, and that are releasable by means (8) which are activated when the plunger (P) is in an end-of-liquid-injection position.