The syringe 1 has a syringe outer cylinder having an outer cylinder main body 21, a reduced diameter portion 22 provided at a distal end portion of the outer cylinder main body 21, and a lock adapter 6 disposed concentrically on the outer peripheral portion of the reduced diameter portion 22. 2 and a cap body 7 that is attached to the syringe outer cylinder 2 and seals the reduced diameter portion 22 in a liquid-tight state in the attached state, and is disposed on the proximal end side of the cap body 7 and attached to the outer peripheral portion of the lock adapter 6 And a cap 5 having a rupture portion 9 that connects the cap body 7 and the attachment portion 8 and can be released by rupture, and the cap body 7 is formed to project toward the base end side. The inner ring 74 and the outer ring 75 are arranged concentrically, and in the mounted state, the inner ring 74 is positioned between the reduced diameter portion 22 and the lock adapter 6 in a loosely fitted state, The outer ring 75 is loosely fitted on the outside of the lock adapter 6 It is located.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。
