PURPOSE: To obtain high reliability against mis-operation by employing a prescribed slider operated corresponding to insertion of a key for a door or the like.

CONSTITUTION: An inner housing 7 inserted in a lock housing 1 has guide plates 8, 9 arranged for a slider 6 and when a key 5 is inserted between the plates 8, 9, the plate 8 is bent toward a bottom 11. The slider is forwarded only by the insertion of a normal key 5. The slider 6 has connected turnable carriers 24-27 and each carrier is provided with code conversion magnets 28-31. A permanent magnet 15 and the magnets 29-31 are displaced so as to be escaped from a lock hole 13 by the key 5 and the slider 6 is moved in a direction (y) while being connected to a rotary knob 2. The magnet 28 goes into a longitudinal groove 34 to realize a desired roll.