PURPOSE: To give any third party an acknowledgement that a lock concerned is of such a type as opened only with symbol system and heighten the confidentiality of the lock by furnishing a symbol system which is not related any to opening of the lock, and concealing the key hole with a blocking plate, etc.

CONSTITUTION: Rotary rings 4, 5, 6 are installed at the periphery of a lock device 1 in such a way as not related to opening of a lock element 10. The lock device 1 is fitted with a blocking plate, etc., to block the key hole 12 so that existence of the hole 12 is concealed. To open the lock 10, a key 11 is inserted through the key hole 12 and rotated for opening. Thus the symbol system not related any to opening of the lock 10 is furnished on the lock body 1 so that a third party misunderstands and tries to interpreting for opening, which should hinder the lock 10 from being opened.