Needleless injection device (10) comprising an injection system (28) which extends axially along an injection axis (B) and which comprises at least upstream towards downstream following the direction of injection: at least one piston (32, 34), - a tank (24) containing an active ingredient (26) and having a lower face (38), - an injection nozzle (28) that is axially delimited by an upper face (60) arranged opposite the lower face (38) of the tank (24), and a lower face (62) adapted to cooperate with an operculum (64), delimiting the nozzle (28) at least one channel (72) of injection extending globally axially from the top face 60, to the bottom face 62 of the nozzle 28, - a top seal 78 extending around at least one channel ( 72) and that is housed in an upper slot (80) arranged on the upper face (60) of the nozzle (28), and said joint (78) being designed to be axially supported on the lower face (38) of the tank (24), characterized in that the upper joint (78) has a wave-shaped radial section that successively comprises, according to a radial direction , a hollow portion (86) and a protruding portion (88), said protruding portion (88) being suitable for lying down towards the hollow portion (86) provided for this purpose, under the effect of the axial pressure exerted on the lower face (38) of the tank (24) on said sealing gasket (78).Dispositivo (10) de inyección sin aguja que comprende un sistema de inyección (28) que se extiende axialmente según un eje (B) de inyección y que comprende por lo menos, de aguas arriba hacia aguas abajo siguiendo el sentido de inyección: - por lo menos un pistón (32, 34), - un depósito (24) que contiene un principio activo (26) y que presenta una cara inferior (38), - una boquilla (28) de inyección que está delimitada axialmente por una cara superior (60) dispuesta frente a la cara inferior (38) del depósito (24), y una cara inferior (62) adaptada para cooperar con un opérculo (64), delimitando la boquilla (28) por lo menos un canal (7
