PURPOSE: To prevent the occurrence of a burglar by a method wherein when a key is inserted in a key hole, a first tubular is retracted in a cylinder to release engagement with a lock device body, a second tubular is protruded outwardly of the cylinder and engaged with the engaging recessed part of a working shaft.

CONSTITUTION: When a key 21 is inserted in a key hole 22 and a cylinder 20 is rotated from an OFF-position to a lock position, movement of the cylinder 20 is transmitted to a working shaft 33 through a second tubular 61. Rotation of the working shaft 33 is converted into linear movement and transmitted to a lock bar 52, the lock bar 52 is protruded from a housing 12 and hooked to a lock hole 55 of a stopper metal 54. When the key 21 is pulled off from the key hole 22, a first tubular 24 is protruded from the outer peripheral surface of the cylinder 20 and hooked in a second engaging groove 31, and a front fork is maintained in a lock state. The second tubular 61 is retracted in the cylinder 20 except for insertion of the key 21 into the key hole 22, and engagement with an engaging groove 64 of the working shaft 33 is rendered ineffective.