A syringe comprises a needle cylinder, a needle base, an intermediate member and a pushing handle. The needle cylinder is hollow at both ends and has a ring groove formed on an inner wall thereof. The needle base, which is located in the needle cylinder to seal one end of the needle cylinder, comprises a pressurizing part and a first hook part having a hook surface. The intermediate member located in the needle cylinder comprises a protruded wall having a distal end portion located in the ring groove and a first combination part. The protruded wall of the intermediate member has a pressurized part which is in contact with the pressurizing part of the needle base. When the pressurized part of the protruded wall is exerted by the pressurizing part of the needle base, an outer wall of the distal end of the protruded wall is driven to pressurize on the inner wall of the ring groove. A first portion of the pushing handle is located inside the needle cylinder, and a second portion of the pushing handle is located outside the needle cylinder. The pushing handle has a second combination part that is combined with the first combination part of the intermediate member when the pushing handle is located at a predetermined position of the needle cylinder, thus to make the pushing handle link with the intermediate member.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。1‧‧‧注射器10‧‧‧針筒14‧‧‧內環齒20‧‧‧針座22‧‧‧通孔24‧‧‧施壓部28‧‧‧外環齒30‧‧‧中介件32‧‧‧環體34‧‧‧凸垣36‧‧‧第二勾部38‧‧‧檔板40‧‧‧推柄42‧‧‧第二結合部42a‧‧‧凸錐部42b‧‧‧頸部44‧‧‧推柄本體46‧‧‧擋止端48‧‧‧折斷處60‧‧‧O型環70‧‧‧活塞
