The purpose of the present invention is to provide a cylinder lock having excellent anti-theft properties and which does not readily become inoperable as a result of tampering, etc. The cylinder lock has a plug (3) capable of rotation operation using an authentic unlocking key, said plug (3) being inserted inside a plug insertion hole (2) in a case (1). Provided in the case (1) are: a first restricting section (5) that locks to a first stopper (4) formed in a front end section of the plug (3) and restricts movement of the plug (3) towards the rear; and a second restricting section (7) that locks, as a result of the plug (3) moving towards the rear, to a second stopper (6) formed in a rear end section of the plug (3) and restricts the rotation of the plug (3). A fuse section (8) that breaks as a result of a prescribed torsional load is provided in an intermediate section between the first stopper (4) and the second stopper (6) in the plug (3).