An autoinjector comprising a lower body receiving a tank, said tank containing fluid product and comprising a piston and a needle, such as a pre-filled syringe, said autoinjector comprising: • an actuating sleeve provided with a contact end designed to make contact with the body of the user, said actuating sleeve being moveable between projected positions and an actuation position, said actuating sleeve being in a first projected position prior to actuation of the autoinjector and in a second projected position after actuation of the autoinjector; • injection means (1005, 1008) adapted to inject said fluid product through said needle when said needle is in the injection position, said injection means comprising a piston rod adapted to cooperate with the piston of said tank, a support pellet provided with at least one deformable foot and an injection spring, said piston rod being moveable between a loaded position and an injection position in which said piston rod has moved the piston of the tank to inject the fluid product through the needle, said injection spring cooperating with said piston rod and said support pellet to urge said piston rod towards its injection position; • an injection lock adapted to block said injection means (1005, 1008); • a spring of the actuating sleeve adapted to automatically return said actuating sleeve to said second projected position when the user removes the autoinjector from his body, said actuating sleeve being locked in this second projected position, preventing any other actuation of the autoinjector; said autoinjector comprising an external shell comprising at least one display window (1221; 1023) for indicating visually to the user the actuation sequences of the autoinjector; characterized in that said external shell comprises at least one other display window indicating to the user that the injection of the fluid product is finished by showing said at least one deformable foot of said support pellet, said at least one display window being formed in the distal end edge of said external shell, by being evident at the same time in the axial direction and in the radial direction of said external shell. • an actuating sleeve provided with a contact end designed to make contact with the body of the user, said actuating sleeve being moveable between projected positions and an actuation position, said actuating sleeve being in a first projected position prior to actuation of the autoinjector and in a second projected position after actuation of the autoinjector; • injection means (1005, 1008) adapted to inject said fluid product through said needle when said needle is in the injection position, said injection means comprising a piston rod adapted to cooperate with the piston of said tank, a support pellet provided with at least one deformable foot and an injection spring, said piston rod being moveable between a loaded position and an injection position in which said piston rod has moved the piston of the tank to inject the fluid product through the needle, said injection spring cooperating with said piston rod and said support pellet to urge said piston rod towards its injection position; • an injection lock adapted to block said injection means (1005, 1008); • a spring of the actuating sleeve adapted to automatically return said actuating sleeve to said second projected position when the user removes the autoinjector from his body, said actuating sleeve being locked in this second projected position, preventing any other actuation of the autoinjector;