PROBLEM TO BE SOLVED: To provide a syringe which is excellent in tamper proof property and can prevent unintentional breakage of a breakage part.SOLUTION: A syringe 1 comprises: a syringe outer cylinder 2 having an outer cylinder body 21, a reduced-diameter part 22 provided at a distal end part of the outer cylinder body 21, and a lock adapter 6 concentrically disposed on an outer peripheral part of the reduced-diameter part 22； and a cap 5 having a cap body 7 mounted to the syringe outer cylinder 2 and sealing the reduced-diameter part 22 in a fluid-tight manner in the mounted state, a mounting part 8 disposed on a base end side of the cap body 7 and mounted to an outer peripheral part of the lock adapter 6, and a breakage part 9 connecting the cap body 7 and the mounting part 8 and capable of releasing the connection by breaking. The cap body 7 has an inner ring 74 and an outer ring 75 which are formed to protrude toward the base end side and arranged concentrically. In the mounted state, the inner ring 74 is located between the reduced-diameter part 22 and the lock adapter 6 in a loosely fitted state, and the outer ring 75 is located outside the lock adapter 6 in the loosely fitted state.SELECTED DRAWING: Figure 3【課題】タンパープルーフ性に優れ、かつ、破断部の不本意な破断を防止し得るシリンジを提供すること。【解決手段】シリンジ１は、外筒本体２１と、外筒本体２１の先端部に設けられた縮径部２２と、縮径部２２の外周部に同心的に配置されたロックアダプタ６とを有するシリンジ外筒２と、シリンジ外筒２に装着され、その装着状態で縮径部２２を液密に封止するキャップ本体７と、キャップ本体７の基端側に配置され、ロックアダプタ６の外周部に装着される装着部８と、キャップ本体７と装着部８とを連結し、その連結を破断により解除可能な破断部９とを有するキャップ５とを備え、キャップ本体７は、基端側に突出形成され、同心的に配置された内リング７４と外リング７５とを有し、前記装着状態で、内リング７４は、縮径部２２とロックアダプタ６との間に遊嵌状態で位置するとともに、外リング７５は、ロックアダプタ６の外側に遊嵌状態で位置する。【選択図】図３
