A stopper structure includes a wall defining an opening. A rotary electronic component has a rotational shaft extending through the opening. A channel stopper has a tubular body and an engagement projection. The tubular body is detachably mounted onto the rotational shaft and is inhibited from rotating relative thereto. The engagement projection extends from an end of the tubular body in an axial direction and a radial direction with respect to the rotational shaft. A rotary operation member is detachably mounted onto the rotational shaft and the tubular body and is inhibited from rotating relative thereto. The rotary operation member has an axial hole in which at least portions of the rotational shaft and the tubular body fit. A limiting portion provided on the wall is engageable with the engagement projection for limiting a range of rotation of the rotational shaft.