This creation provides a kind of syringe (one), includes: a syringe, a push rod, a needle holder and a retaining part. The inside wall surface system of the syringe is equipped with a chase. The push rod system actively wears in the what syringe, and the front end of the push rod is equipped with a piston. The what syringe front end is arranged in the needle holder system. The retaining part system is correspondingly arranged the what chase. Wherein, which actively links the what needle holder, and when the push rod and the needle holder system are together toward moving inside the syringe, which supports the what retaining part and can not exit. Thereby, this creation syringe what retracts Hou, can avoid push rod and is persistently drawn out outside what syringe, causes antihygienic situation that falls off, avoid the case where reusing or hurting sb.'s feelings.本創作提供一種注射器(一)，包括有：一針筒、一推桿、一針頭座及一止退件。該針筒的內部壁面係設有一凹溝。該推桿係活動地穿設於該針筒內，該推桿的前端設有一活塞。該針頭座係設置於該針筒前端。該止退件係對應設置於該凹溝。其中，該推桿係活動地連結於該針頭座，當該推桿與該針頭座係一併地往該針筒內部移動，該推桿係抵頂於該止退件而無法退出。藉此，本創作注射器於拉回後，可避免推桿持續被拉出於針筒外，造成脫落不衛生的情況，避免重複使用或傷人的情況。
