To provide a cylinder lock that is simple in structure but difficult to unlock.

The locking device is provided with the second engaging means that prohibits the rotation of an internal cylinder 3 with respect to the external cylinder by advancing into a key insertion portion 21 under the urging of a spring 7 through a guide hole 16 penetrating the peripheral wall of an external cylinder 2 in the direction crossing the axial direction of the external cylinder 2 and communicating crosswise with the key insertion portion 21 and has an engaging pin 5 that presses out the key insertion section 21 against the urging of a spring 7 by the vicinity of the tip of the key insertion section 21 extending to the terminal end side from the first engaging means of a key 6A inserted into the key insertion section 21 between the first engagement means and the terminal end of the key insertion section 21 of an internal cylinder 3, and a remote control means connected to the engaging pin 5 to withdraw out the key insertion section 21 by pulling the engaging pin 5 against the urging of the spring 7.