This creation provides a kind of syringe (two), comprising: a syringe, a push rod and a needle holder. The holding part of the mobile accommodating what syringe of push rod and the front end for supporting syringe, the push rod front end are equipped with piston and protrude the connection pillar of what piston, and the surface that connects pillar has ring block, annular groove, blocking part and butting section； The front end of needle holder installing what syringe. Wherein, the block holder of transition part clip corresponding with the clipping block system of hollow wedge makes the fixed what conehead component of hollow wedge. The butting section outer diameter of the whats such as the socket part internal diameter through conehead component inside connection pillar, to connect pillar energy tight abutment what socket part, simultaneously, link what blocking part by resilient barb clip, so that push rod what injection Hou can link with needle holder, when pull back push rod when, needle holder can be retracted in syringe together.本創作提供一種注射器(二)，包括：一針筒、一推桿及一針頭座。推桿移動容置於針筒的容置部且抵頂針筒的前端部，該推桿前端設有活塞及凸出於活塞的連接凸柱，於連接凸柱的表面具有環塊、環槽、卡掣部及抵靠部；針頭座裝設於針筒的前端部。其中，過渡部的卡掣體與空心楔件的卡掣塊係對應卡掣，使空心楔件固定於錐頭構件。透過錐頭構件內部的套接部內徑等於連接凸柱的抵靠部外徑，以便連接凸柱能緊密抵靠於套接部，同時，藉由彈性倒鉤卡掣連結於卡掣部，以便推桿於注射後可以與針頭座連結，當回拉推桿時，可以一併將針頭座拉回針筒內。
