To polish a projecting part such as a bolt or the like for fixing a roof in a short time by forcing plural polishing members to be rotated on its axis and revolved round the projecting part to be polished by a polishing member driving means.

Three wire brushes 31 as a polishing member are disposed with the peripheral surfaces close to each other a little spaced from each other on the lower end part of a brush holding shaft 27 to form a space 33 surrounded by the wire brushes 31. A polishing member driving means is formed by a holder 15, a fixing shaft 21, a sun gear 23, a brush holding shaft 27 and three pinion gears 29. By rotary driving force of a driving shaft 5, the holder 15 is rotated through the fixing shaft 21, whereby the pinion gears 29 are rotated to rotate the brush holding shaft 27. Thus, a bolt 67 put in the space 33 is polished. The holder 15 is rotated and the wire brushes 31 themselves are rotated so that the bolt 67 can be polished in a short time.