This creation provides a kind of syringe, comprising: a syringe, one movably accommodate the connector of needle core bar and a setting what needle core bar inside the what syringe. Wherein, the front end system of the needle core bar is equipped with a connecting column, which is equipped with the accommodation groove of a holding slot and the two connection what holding slots, and the holding slot system has an at least convex block, which is correspondingly arranged the what holding slot and is fixed by the convex block. So； the syringe of this creation can pull back safely and set the syringe needle of what syringe front end, by the holding slot that connector is consolidated to setting what connecting column, it can be ensured that certainty when pulling back； deficiency of the existing this kind of safety injector on structure-design technique is overcome, a possibility that reusing can be effectively prevented.本創作提供一種注射器，包括：一針筒、一可活動地容置於該針筒內部的針芯杆、以及一設置於該針芯杆的連接件。其中，該針芯杆的前端係設有一連接柱，該連接柱係設有一固持槽及二連通於該固持槽的容置槽，且該固持槽係具有至少一凸塊，該連接件係對應設置於該固持槽且受該凸塊所固定。如此，本創作之注射器可安全回拉設於針筒前端的針頭，藉由將連接件穩固設置於連接柱的固持槽，可確保回拉時的確實性，克服了現有這類安全注射器在結構設計技術上的不足，能有效杜絕重復使用的可能性。
