Abstract: This device for an injection syringe including a cylindrical body (2) closed at one of its ends by a transverse wall in which the needle (6) is implanted, is such that the end of the cylindrical body is fitted with a slideway (7) for a needle protector (8) that includes a first tubular portion (9) of large diameter suitable for sliding along the slideway (7) between two positions that are axially separate from each other, and a small diameter portion (10) that extends the large diameter portion longitudinally, forming a moving protective sheath for the end of the needle (6), guiding and indexing elements (11, 12, 14, 16, 22, 26) being provided in inaccessible manner between the slideway (7) and the large diameter portion (9) of the protector so as to allow the needle to be uncovered and then recovered in succession once only.