PURPOSE: To make it possible to prevent a key device exactly from a violent breaking and unjust unlocking by fastening a lock of a shaft against a cylinder case, and releasing the locking of a rotor against the shaft when a key is pulled out of a keyhole.

CONSTITUTION: A shaft 2 is housed in a hollow section 3 of a cylinder case 1, and a rotor 4 is housed in a hollow section 5 of the shaft 2 so that they are capable of rotating by preventing the movement in the direction of their shafts. After that, a driver pin 9, cord pin 10 and tumbler pin 11 are successively housed in pin-holes 6, 7 and 8 of the cylinder case 1, shaft 2 and rotor 3, and they are slid and energized by springs 12. When a key 14 is inserted into a keyhole 13, the locking of the shaft 2 against the cylinder case 1 is released, and a lock of the rotor 4 against the shaft 2 is fastened. When the key 14 is pulled out of the keyhole 13, a lock of the shaft 2 against the cylinder case 1 is fastened, and the lock of the rotor 4 against the shaft 2 is released.