Abstract: An automatic injector device operating stroke-by-stroke, comprising a frame whose shape is substantially similar to that of a revolver, a removable injection syringes comprising a syringe body, a syringe piston and at least one injection needle, a syringe-cradle carrying the said syringe and itself supported by the said frame, drive means on the one hand actuating in reciprocating motion the cradle-syringe assembly, and on the other hand actuating the syringe piston, and means for manually starting at least one injection, such as for example a trigger, which operates at least a part of said drive means.