The device for injecting a liquid product is intended to receive an injection syringe comprising a syringe body, carrying an injection needle, and a piston mounted axially sliding in the syringe body in the distal direction when an injection is performed. The injection device comprises a piston control member intended to cooperate axially, under the effect of an elastic force, with a piston rod, linked kinematically to the piston in order to make same slide. The injection device further comprises at least one deceleration member, said deceleration member being kinematically linked, in the movement of same in translation along the injection axis X, to the piston control member, the deceleration member being mounted movable in a positioning control member (20) with which it cooperates via a deceleration cam/deceleration cam path (102, 104) contact, one of the deceleration cam and the deceleration cam path (102, 104) being carried by the deceleration member and the other by the positioning control member (20), the deceleration cam path (102, 104) comprising a so-called injection portion (102D, 104D) such that, when the deceleration cam it passes through this injection portion, the piston control member causes the piston to slide, the injection portion (102D, 104D) of the deceleration cam path (102, 104) comprising at least two sections referred to respectively as fast (102R, 104R) and slow (102L, 104L), with different inclinations.
