To provide a thumb turn structure which allows a security function for restricting the rotation of a knob part to be maintained in a release state without use of a separate member.

A thumb turn structure comprises: a first button 39 and a second button 41 having respective central parts rotatably supported around a swing shaft 59, separate front swing arms 69 projecting from the external surface 71 of a knob part 15, and rear swing legs 73 to swing for releasing the restriction of an internal thumb turn rotation-restricting mechanism when the front swing arms 69 are pushed in; a switch member 87 slidably disposed at the first button 39; and an engaging part 89 which is disposed at the second button 41 and engages the switch member 87 slid to one slide position for holding the first button 39 and the second button 41 at pushed-in positions when the first button 39 and the second button 41 are pushed in.