A kind of syringe includes: a syringe, a needle stand, an intermediate piece and a push handle. Syringe is both ends transmission, and has an annular groove on its inner wall. End of one of in the what syringe of needle stand position and closing syringe, has more a pressure unit and one first hook part, and the first hook part has a hook surface. In the what syringe of intermediate piece position, and there is a convex parapet, and in the distal portion what annular groove of convex parapet； Convex parapet has a compression zone, is to contact with the pressure unit of needle stand, in the pressure bestowed by pressure unit, can promote the end outer wall pressure what annular groove inner wall person of convex parapet. In a part of position what syringe of push handle, outside the what syringe of another part position； Push handle has one second engaging portion, combines the first engaging portion when one of tying up in the what syringe of push handle position predetermined position, push handle is enable to interlock intermediate piece person.一種注射器包含：一針筒、一針座、一中介件以及一推柄。針筒為兩端透空，且其內壁上具有一環槽。針座位於針筒中並封閉針筒之一端，其更具有一施壓部及一第一勾部，且第一勾部具有一勾面。中介件位於針筒中，並具有一凸垣，且凸垣之末端部位於環槽中；凸垣具有一受壓部，係與針座之施壓部接觸，用以在受到施壓部所施予之壓力時，可促使凸垣之末端外壁施壓於環槽內壁者。推柄之一部分位於針筒中，另一部分位於針筒外；推柄具有一第二結合部，係在推柄位於針筒內之一預定位置時結合第一結合部，使推柄得以連動中介件者。
