The injection syringe (12) comprises a syringe body (14) having an injection needle (28) and a piston, the safety device (10) comprising - a syringe holder, comprising means for fixing the syringe body (14) on the syringe holder, said first fixing means, - a protective sheath (34), the syringe holder and the protective sheath (34) being axially slidably mounted, one for each relative to each other between an injection position, during which the injection needle (28) protrudes from the protective sheath (34), and a protective position, during which the injection needle (28) is covered by the protective sleeve (34), - a piston rod (18) configured to be attached to the piston (20), - a retaining member (50) of the piston (20) configured to be attached. on the syringe holder from the proximal end (1 OP) once the syringe body (14) is assembled into the syringe holder, the retainer (50) defining a passage opening (52) of the plunger rod (18) having a shape preventing withdrawal of the plunger (20) from the syringe body (14) and also comprising means for fixing the retaining member (50) on the syringe holder, said second fixing means (54), these second fixing means (54) providing additional retention of the syringe body (14) in the holder syringe, to be added to the restraint provided by the first attachment means. La seringue d'injection (12) comprend un corps de seringue (14) muni d'une aiguille d'injection (28) et d'un piston, le dispositif de sécurité (10) comprenant - un support de seringue, comprenant des moyens de fixation du corps de seringue (14) sur le support de seringue, dits premiers moyens de fixation, - un fourreau de protection (34), le support de seringue et le fourreau de protection (34) étant montés coulissants axialement l'un par rapport à l'autre entre une position d'injection, au cours de laquelle l'aiguille d'injection (28) dépasse du fourreau de protection (34), et une position de protection, au cours de laquelle l'aiguill
