To provide a thumb-turn device for a lock which can hardly be unlocked illegally by preventing a thumb-turn shaft from being turned in an unlocking direction even if a couple of right/left forces equivalent to each other is applied on the thumb-turn knob by an illegally unlocking tool to turn the thumb-turn shaft in the unlocking direction, and to provide a door lock.

The thumb-turn device for the door lock comprises a cover body (thumb-turn) 20 provided on the front part of the thumb-turn shaft 14, a clutch mechanism 30 provided between the cover body 20 and the front part of the shaft 14 and an urging device 31 normally giving an urging force to keep an engaging member 23 of the clutch mechanism 30 and a member 146 to be engaged disengaged from each other. Normally, the engaging member 23 and the member 146 to be engaged are kept disengaged from each other by the urging force of the urging device 31 so that the cover body 20 can be rotated with respect to the thumb-turn shaft 14. When the lock is unlocked, the cover body 20 is pushed to engage the engagement member 23 and the member 146 to be engaged with each other, and the thumb-turn shaft 14 and the cover body 20 are turned integrally with each other in a locking or an unlocking direction.