The present invention provides a kind of syringe, and Hou gear function is realized using the blade of a sword portion of the position of position what base end side more than gasket and is used while seeking to ensure air-tightness, can sufficiently carry out sterilization treatment in the state that the plunger rod for being formed with blade of a sword portion is assembled. Gasket (3) are put by the cardinal extremity opening (22) of cylinder (2), next is put into plunger rod (4) and makes it combine what front end, then finger grip (5) are installed what flange (23). Round plate (45) are formed on leaving plunger rod of the gasket towards the position of base end side, the peritreme (521) of only what finger grip can be supported. The outer peripheral edge portion of round plate (45) forms the connection opening portion (451) of concavity. When what uses hydrogen peroxide gas sterilization treatment, entering the hydrogen peroxide gas of open space (26) by cardinal extremity opening, also negotiable what substantially confined air is asked in (25) via connection opening portion.本發明提供一種注射器，其使用比墊片更位於基端側之位置的鍔部而實現後擋機能並藉以在謀求確保氣密性的同時，能夠在形成有鍔部之柱塞桿被組裝的狀態下充分進行滅菌處理。由筒(2)之基端開口(22)放入墊片(3)，其次放入柱塞桿(4)使其結合於前端，再將指握件(5)裝設於凸緣(23)。在離開墊片朝基端側之位置之柱塞桿上形成圓盤部(45)，使其能抵止於指握件之孔緣(521)。圓盤部(45)之外周緣部形成凹狀之連通開口部(451)。於使用過氧化氫氣體滅菌處理時，由基端開口進入開放空間(26)之過氧化氫氣體經由連通開口部亦可流通於大致密閉空問(25)內。
