A syringe is provided with a syringe outer tube having a spout, and a cap mounted to the spout. The cap is provided with a cap main body which seals the spout in a liquid-tight manner, a ring-shaped mounting section which is disposed on the base end side of the cap main body and which is mounted onto the outer circumferential portion of the spout, and a breaking section which links the cap main body and the mounting section and which can release said link by breaking. The inner circumferential portion of the mounting section is formed with a pair of protrusions. The outer circumferential portion of the spout is formed with a groove to which the protrusions are inserted, and which has a tilted section that is tilted in relation to the axis of the outer circumferential portion of the spout. When the cap is rotated along the axial direction of the syringe outer tube, the protrusions move along the tilted section of the groove. As a consequence of said movement, the mounting section is displaced in the base end direction and the braking section is pulled in said direction and breaks, thereby separating the cap main body from the mounting section.
