To provide a lock device and a lock system increased in security by adopting a mechanical locking/unlocking mechanism, so designed that reflected light is emitted from the inside of a lock, and having an optical function for authentication based on whether the reflected light is strong or weak.

The lock comprises a key, a first light emitting element which illuminates the end of the key when the key is inserted into a plug, and a light receiving element which receives the reflected light reflected by the reflecting elements of the key. The key comprises a light guide installed in the longitudinal direction of a metal body, formed of one or more of reflecting elements attached to the light guide at proper positions, and allowing a part of the light directed to the light guide to be reflected by the reflecting elements and emitted from the end of the light guide.