The syringe includes a syringe outer cylinder having a mouth portion and a cap attached to the mouth portion. The cap includes a cap main body that seals the mouth in a liquid-tight manner, a ring-shaped mounting portion that is disposed on the base end side of the cap main body and is attached to the outer peripheral portion of the mouth portion, and the cap main body and the mounting portion. And a breakable portion that can be released by breakage. A pair of protrusions are formed on the inner peripheral portion of the mounting portion, and the outer peripheral portion of the mouth portion is inclined with respect to its axis. A groove into which the protrusion is inserted, and when the cap is rotated around its axis with respect to the syringe outer cylinder, the protrusion moves along the inclined portion of the groove. Due to the movement, the mounting portion is displaced in the proximal direction, and the breaking portion is pulled in the same direction to be broken, and the cap body is detached from the mounting portion.シリンジは、口部を有するシリンジ外筒と、口部に装着されるキャップとを備える。キャップは、口部を液密に封止するキャップ本体と、キャップ本体の基端側に配置され、口部の外周部に装着されるリング状をなす装着部と、キャップ本体と装着部とを連結し、その連結を破断により解除可能な破断部とを備え、装着部の内周部には、一対の突部が突出形成され、口部の外周部には、その軸に対し傾斜した傾斜部を有し、突部が挿入される溝が形成されており、キャップをシリンジ外筒に対しその軸回りの回転操作を行なった際、突部が溝の傾斜部に沿って移動し、この移動により、装着部が基端方向に変位するとともに、破断部が同方向に引張られて破断し、装着部からキャップ本体が離脱する。
