To prevent unlocking even if a thumb turn is illegally rotated and operated by inserting finger, bar or the like inside of an indoor side from a small window broken intentionally.

The thumb turn 7 is so constituted that torque is inputted to a lock box 3 built in a door 1 and that a lock member provided in the inside of the lock box 3 is moved forward and backward to a door frame, and it includes a tongue section 9 exposed to the surface of the indoor side of the door 1 to rotatably fix and formed of a hollow section 23 opened in the end face opposed to the lock box 3, a core member 11 internally provided to the hollow section 23 so as to make it possible to move in the direction of the rotary center shaft of the knob section 9 and so as not to make relative rotation and locked or unlocked to a rotational input section 3a of the lock box 3 and a transfer releasing screw 13 having the head section 13a exposed to the surface of the tongue section 9, at the same time, having the front end screwed in the core member 11 and moving the core member 11 in the direction of the rotary center shaft by rotating the head section 13a.