The present disclosure is directed towards a needleless injection device including an injection system which includes at least one injection nozzle which delimits at least one injection channel, and which is axially delimited by an upper face arranged facing the lower face of the reservoir, and a lower face adapted to cooperate with a cap, and an upper sealing gasket which extends around the at least one channel and which is housed in an upper groove formed on the upper face of the nozzle, and the upper gasket has a wave-shaped radial section which comprises successively, along a radial direction, a recessed portion and a bump portion, said bump portion being adapted to be lying toward the recessed portion provided to this end, under the effect of the axial pressure exerted by the lower face of the reservoir on said sealing gasket.