To prevent deposition of sediment on a lower running body around a rotary device by providing a mud guard plate which rotates around the rotary device on an upper rotary body.

A rotary frame 12 is provided on an upper rotary body 11, and a mud guard plate 20 is installed on the lower surface side of the rotary frame 12. The upper rotary body 11 rotates on a lower running body 1 through a rotation device 7 and the mud guard plate 20 rotates around the rotation device 7 and a round drum 5 in accordance with this rotation action. Deposition of sediments 23 such as soil on a center frame 3 is thus prevented by the mud guard plate 20.