To provide a cylinder lock in which unlocking operation by malfeasant unlocking operation such as a picking is unable.

The cylinder lock has a rotor 3, which is inserted rotatably into a case 1 long in the Z-axis direction and has different axial length in the X-Y axis directions and in which a key inserting hole 2 in which one wall surface opposed to at least an axial center is composed of an outwards projected curved surface is formed in the Z-axis direction, and a case engaging-disengaging means 8 engaging and disengaging engaging-disengaging sections 7 with and from the inner circumference of the case 1 by fitting depth to cord-forming recessed sections 6 on the key plate 5 sides of tumblers 4 forwarded and retracted to and from the key inserting hole 2. The rotor 3 is constituted so as to be able to be rotated and operated by bringing the outer circumferences of key plates 5 capable of being inserted into the key inserting hole 2 into contact with the inner circumference of the key inserting hole 2.