PURPOSE: To simplify operation by performing locking after making a flat plate-like key which is locked with semi-circular holes cut in a long eliptical groove, penetrate the other side of a door and pulling off the key inserted.

CONSTITUTION: In a flat-plate like key a long eliptical groove is formed and two pieces of symmetrical semi-circular holes are cut. In usage, a key 1 is pushed in a key hole, and a lock retaining metal fitting 6 from retaining a square key frame is shifted to the inner side to protrude a square frame 5. At that time the key 1 is pulled over the whole except an eliptical part, and with uneven grip parts on both ends the key 1 is inserted to the other side. A key frame is set at e.g. a door 3, and the square frame 5 is unlocked or removed to make the door 3 open. The door 3 is closed when the key passing to the other side, and by pulling out the key protruding locking conditions are obtained while the door 3 is closed.