To thin a lock main body, and to clarly display locking/unlocking by arranging coloring display parts displayed on one of lock/open display windows of an operation member surface, in a rotor to rotate by 90° by inserting a key into the lock main body.

An inner cylinder 7 to move by a key K is provided in an operation member 1b of a lock main body 1, and a rotor 10 rotates by an L-shaped metal fitting 9 installed in the inner cylinder 7. A shaft 11 is integrally arranged in the rotor 10, and open/lock coloring display parts 12 and 13 are arranged in peripheral opposed positions, and open/lock display window holes 14 and 15 are opened on an upper surface of the operation member 1b. Since the rotor 10 rotates by 90° when the key K is inserted into an inserting hole from the side, the coloring display part 12 or 13 appears from the open display window hole 14, and a T-shaped fastening piece of the rotor 10 slips out of a locking hook part arranged on a base board, so that a lock can be opened by pulling up the operation member 1b. When the coloring display part 12 or 13 appears in the lock display window hole 15 by rotating the rotor 10 further by 90° by inserting the key K by closing the operation member 1b, a lock can be fastened by locking/closing the T-shaped fastening piece by the locking hook part.