PURPOSE: To prevent a handlebar from being caught dangerously during traveling by enabling an engaging part provided on the inner surface of a handlebar pipe having an opening part on the tip to engage an engaging part of a lock body in the state entering the handlebar pipe and releasing the engaging condition by turning a cylinder lock.

CONSTITUTION: After parking a vehicle, a lock body 1 is removed from the body side, a chain 2 is extended to the tip of a handlebar pipe, and a projecting part 12a is inserted into an opening part 4a of the handlebar pipe 4. Then, a lug 13a of an engaging piece 13 in the projecting part 12a abuts against the opening part 4a. Then, the engaging piece 13 is slid to the direction of center by the action of an inclined surface 13d on the tip of the lug 13a against a spring 15. When the lock body 1 is further pushed in, the lug 13a of the engaging piece 13 engages an engaging hole 4a in the handlebar pipe 4 by a force of the spring 15. In unlocking, when a key 3 is inserted and rotated in a rotor 8 of the lock body 1, the engaging piece 13 is disengaged from the engaging hole 4a by a cam 14 interlocked with the rotor 8 and then the lock body 1 is withdrawn.