A syringe includes a syringe outer tube having a spout and a spout-mounted cap. The cap has a cap main body sealing the spout in a liquid-tight manner, a mounting section mounted onto the spout, and a breakable breaking section linking the cap main body and the mounting section to release the link upon breaking. The inner circumferential portion of the mounting section includes protrusions inserted into a groove on the outer circumferential portion of the spout which also has a tilted section tilted relative to the axis of the spout outer circumferential portion. When the cap is rotated along the axial direction of the syringe outer tube, the protrusions move along the tilted section of the groove. The mounting section is thus displaced in the base end direction and the braking section is pulled in the direction and breaks to separate the cap main body from the mounting section.
