To provide a new locking device capable of preventing the loss of a key after the unlocking by preventing the key by coming off from a pivot and incapable of rotating and operating the pivot at an initial position again after the key is used for releasing a locking state to rotate and operate the pivot inside of a key cylinder.

When a key 2 is inserted to rotate a pivot 9 inside of a key cylinder 8 on a direction releasing a locking state, a locking device is equipped with holding mechanisms 12b and 20 for holding a position of the pivot after the rotation and releasing mechanisms 14 and 21 for returning the key 2 to an insertion state by releasing a holding state by the holding mechanisms 12b and 20. Then, when a locking state is released by the holding mechanisms 12b and 20, the key 2 can not be pulled out.