Abstract: The technical field of the invention is that of prefilled and disposable needleless injection devices functioning with a gas generator and used for intradermal, subcutaneous and intramuscular injections. The invention relates to a needleless injection device (1) comprising a pyrotechnic gas generator (2), at least one piston (13, 14), a reserve of liquid active principle (9), and an injection nozzle (11). The principal characteristic of this device is that said generator (2) comprises a pyrotechnic charge (4) composed of a central energetic material which is surrounded by a second peripheral energetic material, the two energetic materials having different rates of combustion.