A syringe includes a syringe outer tube including a tubular-shaped outer tube main body configured to be filled with a liquid, a reduced diameter section located at a distal end of the outer tube main body in a projecting manner, and configured to allow the liquid to pass therethrough, the reduced diameter section having an outside diameter that is smaller than a diameter of the outer tube main body, and a ring-shaped lock adapter concentrically disposed at an outer circumferential portion of the reduced diameter section and configured to fix a mating member connected to the reduced diameter section； and a cap including a cap main body mounted on the syringe outer tube and configured to seal the reduced diameter section in a liquid-tight manner when the cap main body is in a mounted state, a ring-shaped mounting section disposed at a proximal end side of the cap main body and mounted on an outer circumferential portion of the lock adapter, and a breaking section that forms a link between the cap main body and the mounting section and that is configured to release the link by breakage.
