To provide an anticrime thumb-turn minimized in the number of parts.

This anticrime thumb-turn comprises a movable seat having a shaft part extending through the shaft hole of a fixed seat, so installed as to be overlapped with the surface of the fixed seat, and circumferentially rotatable at a predetermined position, a knob fitted to the movable seat and rotatable together with the movable seat when unlocked, and a lock mechanism for preventing the knob and the movable seat from corotating when locked. The lock mechanism comprises a knob locking arm extending to the lock hole of the fixed seat through the through-storage hole of the movable seat, a biasing body support body installed at the insertion end part of the locking arm, and a biasing body elastically installed between the rear surface of the head part of the support body and the biasing body support surface of the through storage hole. When unlocking the lock mechanism, the knob is pulled out to the position where the locking arm support body is extracted from the lock hole against the spring force of the biasing body.