The invention relates to an autoinjector comprising a vessel (S) containing a fluid product and comprising a piston, said autoinjector comprising a piston rod (5) suitable for engaging with the piston of said vessel (S), said piston rod (5) being movable between an inoperative position and an injection position in which said piston rod (5) has moved the piston such as to inject the fluid product, an actuation spring (6) being provided such as to bias said piston rod (5) into the injection position thereof, the autoinjector including a force-adjustment system (7, 8) suitable for exerting at least one force (F2) on said piston rod (5), said force (F2) adding to the force exerted by said spring (6) on said piston rod (5) at the start of the injection, said system including two pivoting members (7) engaging with said piston rod (5), connected to one another by two resilient elements (8), at least one pivoting member (7) being blocked prior to actuation by a locking system (200), thus blocking the actuation of the autoinjector, said autoinjector comprising an unlocking element (101) suitable for moving and/or deforming said locking system (200) in order to unblock said at least one pivoting member (7).Autoinjecteur comportant un réservoir (S) contenant du produit fluide et comportant un piston, ledit autoinjecteur comportant une tige de piston (5) adaptée à coopérer avec le piston dudit réservoir (S), ladite tige de piston (5) étant déplaçable entre une position de repos et une position d'injection dans laquelle ladite tige de piston (5) a déplacé le piston pour injecter le produit fluide, un ressort d'actionnement (6) étant prévu pour solliciter ladite tige de piston (5) vers sa position d'injection, l'autoinjecteur comprenant un système de réglage de force (7, 8) adapté à exercer au moins une force (F2) sur ladite tige de piston (5), ladite force (F2) s'ajoutant à la force exercée par ledit ressort (6) sur ladite tige de piston (5) en début d'injection, ledit système c
