An autoinjector comprising: • a body receiving a reservoir, said reservoir containing fluid and including a piston, such as a pre-filled syringe, • a piston rod that is adapted to co-operate with the piston of said reservoir, said piston rod being movable by an injection spring between a primed position and an injection position in which said piston rod has moved the piston of the reservoir so as to inject the fluid into an injection site, • a visual, audible, and/or tactile indicator device for indicating to the user that said autoinjector may be removed from said injection site, said autoinjector it including a retarding system for delaying the actuation of said visual, audible and/or tactile indicator device relative to the end of injection, said retarding system including a dashpot containing a fluid, a piston being arranged in said dashpot, one of said dashpot and of said piston being movable in translation in said body during actuation of said retarding system, and the other of said dashpot and of said piston being stationary relative to said body during actuation of said retarding system, the movement in translation of one relative to the other moving said fluid out from said dashpot, through at least one flow passage (161; 195), such that said movement in translation is braked, said retarding system comprising said dashpot containing said fluid, said piston, a locking key, said injection spring, a pusher element, a support member interposed between said pusher element and said injection spring, and said piston rod, characterized in that said locking key comprises a head, a longitudinal rod, and an endpiece that is adapted to co-operate with the piston rod, said head of the locking key, being in its blocking position before triggering the retarding system, in which position it co-operates with a recess of said pusher element, said piston rod, when it arrives towards its end-of-injection position, co-operating with the endpiece of the locking key so as to pull said locking key axially downwards out from its blocking position, such that said pusher element is thus no longer prevented from moving in translation by said locking key. • a body receiving a reservoir, said reservoir containing fluid and including a piston, such as a pre-filled syringe, • a piston rod that is adapted to co-operate with the piston of said reservoir, said piston rod being movable by an injection spring between a primed position and an injection position in which said piston rod has moved the piston of the reservoir so as to inject the fluid into an injection site, • a visual, audible, and/or tactile indicator device for indicating to the user that said autoinjector may be removed from said injection site, said autoinjector it including a retarding system for delaying the actuation of said visual, audible and/or tactile indicator device relative to the end of injection, said retarding system including a dashpot containing a fluid, a piston being arranged in said dashpot, one of said dashpot and of said piston being movable in translation in said body during actuation of said retarding system, and the other of said dashpot and of said piston being stationary relative to said body during actuation of said retarding system, the movement in translation of one relative to the other moving said fluid out from said dashpot, through at least one flow passage (161; 195), such that said movement in translation is braked, said retarding system comprising said dashpot containing said fluid, said piston, a locking key, said injection spring, a pusher element, a support member interposed between said pusher element and said injection spring, and said piston rod, characterized in that said locking key comprises a head, a longitudinal rod, and an endpiece that is adapted to co-operate with the piston rod, said head of the locking key, being in its blocking position before triggering the retarding system, in which position it co-operates with a recess of said pusher element, said piston rod, when it arrives towards its end-of-injection position, co-operating with the endpiece of the locking key so as to pull said locking key axially downwards out from its blocking position, such that said pusher element is thus no longer prevented from moving in translation by said locking key.