The present invention provides a positioning device for syringe. The positioning device includes a communicating tube, a membrane, a first joining part and a second joining part. The communicating tube includes a first opening, a second opening and a third opening. The first opening connects a needle. The third opening connects a needle cylinder. The membrane is disposed on the second opening. The first joining part is fitted co-axially over the communicating tube, and the second joining part is connected to the membrane. When the pressure drops down within the communicating tube and causes the membrane to depress, the first joining part and the second joining part combine with each other or separate from each other.本發明為一種定位裝置,適用於注射器。定位裝置包含:連通管、薄膜、第一接合件及第二接合件。連通管包括第一開口、第二開口及第三開口,第一開口連接針頭,第三開口連接針筒;薄膜位於第二開口;第一接合件套設於連通管之外側;第二接合件連接於薄膜。當連通管內之壓力下降而使薄膜凹陷時,第二接合件與第一接合件分離或結合。1‧‧‧注射器10‧‧‧針頭12‧‧‧針筒2‧‧‧定位裝置20‧‧‧連通管22‧‧‧薄膜組件24‧‧‧第一接合件26‧‧‧第二接合件
