An autoinjector having an external shell (1022), a reservoir, a piston, a needle, a piston rod (1005) that is displaceable between a loaded position and an injection position in which the piston rod has displaced the piston of the reservoir to inject the fluid product through the needle, an injection spring (1008) to stress the piston rod towards the injection position, and a mobile element (1004; 1006), the piston rod displaceable relative to the mobile element. The autoinjector also includes an indication device (1500) having a key (1120), and a head part (1122). The mobile element including a deformable tab (1510; 1520), the head part cooperating prior to injection with the deformable tab to prevent any radial deformation, blocking the mobile element relative to the external shell. The piston rod, on completion of injection, exerting traction on the head part causing displacement of the key and enabling radial deformation of the deformable tab and axial displacement of the mobile element.