Abstract: A nut covering device comprises the following: a cover assembly, including an inner cover, outer cover, and a first constraining mechanism; a second constraining mechanism; and a third constraining mechanism. The first constraining mechanism constrains so that there is no relative motion of the outer cover with respect to the inner cover in an axis direction. The second constraining mechanism constrains so that there is no relative motion of the inner cover with respect to the nut member in the axis direction. The third constraining mechanism constrains so that there is no relative motion of the outer cover with respect to the nut member in the axis direction at least in the removal direction. When a circumferential phase of the inner cover and the outer cover is matched with a predetermined specified phase, second and third constraining mechanisms are released, and the cover assembly can be removed from the nut member.