To provide a locking mechanism to be locked and unlocked by engaging a locking lever with a step part of a latch head and disengaging the locking lever from the step part of the latch head, which is surely prevents from being unlocked by an earthquake or vibrations.

In this locking mechanism, a supporting shaft 7 is provided near a latch bolt doubling as a dead bolt, and a leading end of the locking lever 8, one end of which is turnably supported on a first supporting shaft, is urged in the direction of being engaged with the step part of the latch head 4. A horizontal ridge 17 is formed at either of the step part of the latch head and the front end of the locking lever, and a recessed groove 18, which can be engaged with the ridge 17, is formed at the other end thereof. An exciting force is applied to a lock case, so that the latch bolt 1 can be urged in the direction of receding into the lock case, and so that the front end of the locking lever 8 can be urged in the direction of being separated from the step part 6 of the latch head. In this case, the ridge 17 and the recessed groove 18 are meshed with each other, so that the front end of the locking lever cannot be disconnected from the step part of the latch head.