The invention concerns the field of needleless syringes for injecting an active principle for therapeutic purposes. More particularly, it concerns a needleless syringe for injecting an active principle (7) initially set between an injector (1, 10) comprising at least an injection nozzle, said injector being contacted with the skin, and a wall (8) mobile under the effect of a propelling system (9) pressurizing and expelling the active principle through the injector located at the syringe downstream end (2). In order to produce nozzles in a considerable injector thickness and to control the jet coherence distance, said injector (1, 10) comprises at least two elements (3, 4) whereof the contact surfaces (30, 40, 40′) are oriented towards the skin, at least a groove (31, 41, 41′) forming an injection nozzle in the assembly of said elements.