A supporting bracket (35) includes an upright portion (35a) which stands upright on a bottom plate (32) of a rotating frame (31) and a flat portion (35b) which protrudes horizontally from a top end of the upright portion (35a). The supporting bracket (35) is formed integrally with the rotating frame (31). A through hole (35c) is provided in the bottom plate (32) of the rotating frame (31) at a position where the through hole (35c) overlaps the flat portion (35b) of the supporting bracket (35) in plan view.
