PURPOSE: To perfectly freely rotate a key cylinder at unlawfully unlocking a cylinder lock.

CONSTITUTION: This cylinder lock is provided with a latch member 19 movably provided between an engagement position where a key cylinder 16 and a drive member 18 are connected together, and a release member 20 moving the latch member 19 to a separation position at relatively rotating a sleeve 13 against a housing 11. When a regular key is inserted into the key cylinder 16, engagement between the key cylinder 16 and the sleeve 13 is released, the drive member 18 is rotated to a lock position or an unlock position accompanying rotation of the key cylinder 16, because the key cylinder 16 and the drive member 18 are connected together by means of the latch member 18. When a dissimilar key is inserted into the key cylinder 16, the key cylinder 16 and the sleeve 13 are simultaneously rotated in the same direction, engagement between the latch member 19 and the drive member 18 is released by movement of the release member 20.