To provide a thumb-turn device for improving resistance to illicit unlocking operation.

This thumb-turn device operates a lock device 3 for locking and unlocking by rotary operation to an operation knob 1 by projecting the operation knob 1 to the indoor side from a front wall of a body part 2; and has a lock part 5 interposed in an operation force transmitting passage reaching a connecting part 4 to the lock device 3 from the operation knob 1, prohibiting the rotary operation of the connecting part 4 by the operation knob 1 in a lock state and allowing the rotary operation in an unlocking state, and a unlocking part 6 releasing the lock state of the lock part 5. The front wall of the body part 2 is provided with a pushing-down operation member 7 for operating the unlocking part 6 by unlocking operation of causing pushing-down operation against energizing force.