To provide a thumb turn device which makes a thumb turn non-rotatable by single hand operation, and prevents easy unauthentic unlocking operation even if the hand of an outsider is inserted inside a room.

The thumb turn device carries out locking/unlocking operation of a door lock device by rotating the thumb turn 1, and is formed of an operation inhibiting member 2, an energizing means 3, and an inhibition canceling operation section 4. The operation inhibiting member moves between an operable position and an inoperable position to permit/inhibit unlocking operation by the thumb turn 1. The energizing means energizes the operation inhibiting member 2 toward the inoperable position. The inhibition canceling operation section moves the operation inhibiting member 2 toward the operable position against energizing force of the energizing means 3.