A traverse arm 28 includes a first plate 61, a second plate 62, which are arranged to face one another in a direction orthogonal to a traverse direction of the traverse arm 28, and a beam 64, which connects the first plate 61 and the second plate 62 to form a truss structure. Space arranged between the beams 64, which form the truss structure, functions as space 67 (penetration hole) for having air pass through in the traverse direction of the traverse arm 28.