Autoinjector comprising a plunger rod (5) that is to cooperate with a plunger (P) in a reservoir (S) and can move between a loaded position and an injection position, and an injection spring (8) for urging the plunger rod (5) into the injection position. The autoinjector further comprises an injection lock that includes a control sleeve (4) containing the plunger rod (5) and the injection spring (8). The plunger rod (5) includes a radial recess (50) accommodating at least one substantially spherical blocking element (7) which can move between a blocking position and a releasing position and which is urged radially outward by the plunger rod (5) and is retained in the blocking position by a blocking ring (23) that can move relative to the plunger rod (5) in order to release the at least one blocking element (7). A supporting member (6) is mounted in the control sleeve (4), said supporting member (6) comprising a ring (60), one axial side of which is in contact with the injection spring (8) and the other axial side of which supports the at least one blocking element (7). The blocking ring (23) engages with the supporting member (6) while being disengaged from the supporting member (6) by means of the control sleeve (4) when the control sleeve (4) moves axially during actuation of the autoinjector, such that the injection lock is released.Autoinjecteur comportant une tige de piston (5) adaptée à coopérer avec un piston (P) dun réservoir (S), ladite tige de piston (5) étant déplaçable entre une position chargée et une position dinjection, un ressort dinjection (8) étant prévu pour solliciter ladite tige de piston (5) vers sa position dinjection, lautoinjecteur comportant une serrure dinjection comportant un manchon de commande (4) contenant ladite tige de piston (5) et ledit ressort dinjection (8), ladite tige de piston (5) comportant un évidement radial (50) recevant au moins un élément de blocage sensiblement sphérique (7) mobile entre une position de blocage et une p
