To provide a disk cylinder lock which is hard to be unlocked through picking operation, in view of increasing lock-picking crimes.

In this disk cylinder lock, many quadrilateral grooves parallel to the central axis of its outer casing (1), forming a figure of a square-shaped internal tooth ratchet, are prepared inside the outer casing (1) as grooves inside the outer casing (13). The disk cylinder lock is used to lock a mechanism in which a disk (4) including an end (14) aligned with the shape of the grooves inside the outer casing (13) is provided on its inner casing (2).