The present invention improves the weathering performance of a stopper structure preventing inadvertent rotation or a rotated body accommodated in a case. An operation member having a head portion rotated outside the case and a shaft portion inserted into a pipe so as to be movable between a first position and a second position that is outer than the first position. A stopper structure is provided inside the case to prevent rotation of the head portion when the operation member is positioned at the second position, whereas the stopper structure allows rotation of the head portion when the operation member is positioned at the first position.