Device for back injecting an implant into the skin of a subject, said device including a hollow main body to which a hollow needle is fixed, into which the implant is introduced, a secondary body coaxially arranged inside the main body and surrounding the needle, and a piston rod capable of sliding coaxially inside said hollow needle means being provided for allowing the piston rod to maintain its position unchanged with respect to the needle when the back injection device is pressed against the subject's skin to allow the needle to penetrate said subject's skin and when the secondary body retracts inside the main body, and to allow the piston rod to penetrate inside the hollow needle to hold the implant at the required depth in the subject's skin while the hollow needle is being withdrawn from the subject's skin, during which the secondary body exits the main body, said device including means for elastically returning the secondary body out of the main body, wherein the elastic return means which control the exit of the secondary body outside of the main body releases automatically thereby bringing the secondary body to surround again the hollow needle.