The invention relates to an auto-injector having: - a reservoir (110) containing fluid product and a plunger (111), and having a needle (112), - a motor module having: - a body (201), - a plunger rod (210) designed to cooperate with the plunger (111) of said reservoir (110), said plunger rod (210) being movable between a rest position and an injection position, in which said plunger rod (210) has moved the plunger (111) from the reservoir (110) in order to inject the fluid product through said needle (112), - an injection spring (220) for urging said piston rod (210) towards its injection position, - a lock, which blocks said piston rod (210) in the rest position, said lock having a wire (230) connected on one side to said piston rod (210) and on the other side to a toothed winding wheel (240), a locking member (260) cooperating with a tooth (241) of said toothed winding wheel (240), said locking member (260) being movable, in particular pivotable, between a blocking position, it which it prevents the winding wheel (240) from rotating in the direction of the actuating force (Fa) exerted by said injection spring (220) on said piston rod (210), and an actuating position, in which said rotation of the winding wheel (240) is possible, said auto-injector having rearming means (400), such as a crank, for rewinding said wire (230) onto said winding wheel (240), by rotation of said winding wheel (240) in the opposite direction to that in the injection phase.Autoinjecteur comportant : - un réservoir (110) contenant du produit fluide et un piston (111 ), et comportant une aiguille (112), - un module moteur comportant : - un corps (201 ), - une tige de piston (210) adaptée à coopérer avec le piston (111 ) dudit réservoir (110), ladite tige de piston (210) étant déplaçable entre une position de repos et une position d'injection dans laquelle ladite tige de piston (210) a déplacé le piston (111) du réservoir (110) pour injecter le produit fluide à travers ladite aiguille (112),
