PURPOSE: To check locking after going out by incorporating a locking sensor detecting locking, a release sensor detecting release, a buffer, in which detection is stored, and a display section displaying a storage content into a key body.
CONSTITUTION: A locking sensor 1, a release sensor 2, a buffer 3 and a display section 6 are incorporated into a key body. Locking is detected by the locking sensor 1, and stored in the buffer 3, and the storage content is displayed to the display section 4. Release is detected by the release sensor 2, and stored in the buffer 3, and the content is displayed to the display section 4. Accordingly, the display section 4 is viewed after going out, thus checking whether a nor locked.