A syringe 1 includes: a syringe outer tube 2 including an outer tube main body 21, a reduced diameter section 22 provided at a distal end portion of the outer tube main body 21, and a lock adapter 6 concentrically disposed at an outer circumferential portion of the reduced diameter section 22 and a cap 5 including a cap main body 7 mounted on the syringe outer tube 2 and configured to seal the reduced diameter section 22 in a liquid-tight manner when the cap main body is in a mounted state, a mounting section 8 disposed at a proximal end side of the cap main body 7 and mounted on an outer circumferential portion of the lock adapter 6, and a breaking section 9 linking the cap main body 7 with the mounting section 8 and capable of releasing the link by breakage. The cap main body 7 includes an inner ring 74 and an outer ring 75 formed on the proximal end side in a projecting manner and concentrically disposed, and in the mounted state, the inner ring 74 is positioned between the reduced diameter section 22 and the lock adapter 6 in a loosely-fitted state, and further the outer ring 75 is positioned outside the lock adapter 6 in the loosely-fitted state.
