To reduce the number of parts, simplify and miniaturize the structure in a lock where unlocking can be carried out a set number of times.

When a key 42 is turned counterclockwise, a lock body 34 rotates counterclockwise and displaces, effecting locking. When locked, tooth crests 44 of a ratchet wheel 36 just rub against the side of a driving leaf spring 60, not transmitting the rotation of the ratchet wheel 36 to a rotating plate 50. When the key 42 is turned clockwise, as the lock body 34 and the ratchet wheel 36 rotate clockwise, and the tooth crests 44 push the driving leaf spring 60. Therefore, the rotating plate 50 also rotates clockwise. As the tooth crests 54 of the rotating plate 50 brush past the free end of the holding-back leaf spring 80, the holding-back leaf spring 80 never inhibits the rotation of the rotating plate 50.