To provide an illicit unlocking preventive device for improving operability of locking operation and unlocking operation, while preventing illicit unlocking of a door lock by a wire.
This illicit unlocking preventive deice 1 has an inner cylinder 2 integrally fixed to a knob 101 to be put on the knob 101, and a cover 3 rotatably and longitudinally reciprocatably put on the inner cylinder 2. A first meshing part 7 of equally arranging an unevenness along an outer peripheral surface, is projected on an inner surface of the cover 3. A second meshing part 8 of equally arranging an unevenness engaging with and disengaging from the unevenness by reciprocating motion of the cover 3 along an inner peripheral surface, is recessed on a front face 2B of the inner cylinder 2. A coil spring 4 for energizing the cover 3 in the direction for releasing engagement with the unevenness of the first meshing part 7 and the unevenness of the second meshing part 8, is arranged between the cover 3 and the inner cylinder 2.
Yukino Koishikawa
Kenta Nitta