To provide a cylinder lock of which the rotor can be simply pulled out and exchanged performed only by inserting a change master key.

A stopper storing hole 12 crossing at the deepest portion of a keyway 3 is formed in a rotor 2, a stopper link-disengage groove 13 is formed to a ring shape on the inner peripheral surface of a fixed external cylinder 1, the tip of the stopper 11 protruded and energized by a spring 14 is linked to the stopper link-disengage groove 13, an edge surface 15a of a key insert hole 15 is pushed by a stopper key code portion formed at the side portion of the farthest tip portion of a change master key 16, and the tip portion of the stopper 11 is disengaged from the stopper disengageable groove 13.