Autoinjector comprising a piston rod (5) adapted to cooperate with a piston (p) of a reservoir (s), said piston rod (5) being displaceable between a loaded position and a position for injection, a spring for injection (8) being provided to urge the piston rod (5) towards its position of the injection, with the auto-injector comprising a lock of injection including a control sleeve (4) containing the said piston rod (5) and the spring of the injection (8), said piston rod (5) comprising a radial recess (50) receiving at least one locking element which is substantially spherical (7) that is movable between a blocking position and an unlocking position, said at least one locking element (7) being urged radially towards the outside by the piston rod (5) and being held in locking position by a locking ring (23) can be moved relative to said piston rod (5) in order to release the said at least one locking element (7), a support member (6) being fixed in said control sleeve (4), said supporting member (6) comprising a ring (60), an axial side is in contact with said spring of the injection (8) and the other axial side supports the said at least one locking element (7), said locking ring (23) being engaged on said support member (6), said locking ring (23) being disengaged from said supporting member (6) by the control sleeve (4) when the control sleeve (4) is displaced axially during the actuation of an auto-injector, in order to unlock the lock for injection.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 radia
