PURPOSE: To confirm the state of locking by installing a mechanism for giving a physical signal which means being locked at the keyhole locking turning end-section of a lock while mounting a mechanism receiving the physical signal to the key side.

CONSTITUTION: A toggle type display mechanism is set up to a key while a magnetic element or a pressure sensitive element for detecting a contact with a lock locking turning-end of the key is installed. An unevenness for the abutting of the toggle mechanism is formed at the lock locking turning-end.