To provide a thumb-turn which serves as a countermeasure against picking of a lock so as to enhance safety, and which is resistant to the fraudulent turning of the thumb-turn.

This thumb-turn 1 comprises at least a thumb-turn shaft 10 which makes a dead bolt advance/retreat via a hub, so as to make the dead bolt protrude from/recede into an end surface of a door, a knob 11 which is engaged with one end of the thumb-turn shaft so as to be turned around the shaft center a of the thumb-turn shaft, a lock idling means 12 which pushes in a driver, capable of advancing/retreating, of the lock by being shifted integrally with the knob in the inward direction of the door along the shaft center of the thumb-turn, so as to disengage the hub from the driver of the lock, when the required tuning of the knob is performed in the engaged state of one end of the knob, and an idling maintaining means 13 for inhibiting the lock idling means and the knob from being shifted in an outward direction opposite to the inward direction of the door in the state of idling the knob.