A fixture is attached to a hollow tube and has a pair of shafts protruding in a width direction. A handle has a base portion and a grip portion located at an end on the outside of the base portion. The base portion has a pair of side portions sandwiching both side surfaces of the fixture. The pair of side portions each have a hole receiving corresponding one of the pair of shafts. A restriction portion of a displacement preventing plate restricts a movement of the side portions in the width direction in a portion of each of the side portions located between an end on the grip portion side of the fixture and an end on the hollow space side of the base portion.