A needleless injection device is provided that includes a body forming a housing, a gas generator, a tubular reservoir that contains an active ingredient, and a T-shaped elastically deformable membrane having a tubular portion. The reservoir extends axially in the housing from an upper end to a lower end and the tubular portion is configured to extend and lie axially in the reservoir under an effect of a pressure generated by the gas generator. An injection nozzle is arranged at the lower end of the reservoir. The tubular portion is funnel shaped and includes at least an upper segment that decreases along an axial elongation direction of the member and a lower segment that increases along the axial elongation direction. The axial length of the upper segment is greater than that of the lower segment.
