PROBLEM TO BE SOLVED: To provide a medical syringe in which a piston does not cause creep deformation even when the piston is charged inside an injection cylinder for a long period to prevent trouble such as reduction in sealing performance of the syringe, liquid medicine leakage or the like accompanying the creep deformation.SOLUTION: In a medical syringe 1, a cylinder body 21 is formed in a nearly cylindrical shape having a small inside diameter part 24 on the tip side, and having a large inside diameter part 25 on the rear end side. A piston 3 is made of a flexible material and is formed in a larger diameter than the inside diameter of the small inside diameter part 24 of the cylinder body 21, and a peripheral part of the piston 3 can be brought into pressure-contact with the inner circumferential face of the small inside diameter part 24 of the cylinder body 21 and is formed in the outside diameter equal to or less than the inside diameter of the large inside diameter part 25 of the cylinder body 21. A plunger rod 4 is held in the center of the cylinder body 21 in a state that the plunger rod 4 is inserted in a rod insertion part of a plunger rod holder 5, and the medical syringe 1 can hold the piston 3 in the large inside diameter part 25 of the cylinder body 21 in a loosely fitting state.COPYRIGHT: (C)2014,JPO&INPIT【課題】ピストンが注射筒の内部に長期間装填される場合でも、ピストンがクリープ変形を起こさず、ひいては前記クリープ変形に伴う注射器の密封性の低下、薬液漏れ等の不具合を防止することができる医療用の注射器を提供する。【解決手段】筒本体21が、先端側に小内径部24を有し、末端側に大内径部25を有する略円筒状に形成され、ピストン3は、可撓性材料からなり、筒本体21の小内径部24の内径より大径に形成され、その外周部が筒本体21の小内径部24の内周面に対して圧接可能に構成されているとともに、筒本体21の大内径部25の内径と同等以下の外径に形成されており、プランジャーロッド4は、プランジャーロッド保持具5のロッド挿入部に挿入された状態で、筒本体21の中心に保持されており、ピストン3を筒本体21の大内径部25に遊嵌状態で保持することを可能とした医療用の注射器1。【選択図】図1
