PURPOSE:To perform effective polishing work by suppressing suction force of an exhaust fan at the initial stage of polishing work and proceeding polishing work while a prescribed time and opening both a bran sucking value and a dust sucking valve at the stage reaching a polished state and discharging chaff, etc. CONSTITUTION:A bran sucking valve 42 is closably provided to a bran sucking cylinder 41 which is opened to a bran sucking duct side form a suction collecting chamber 23. A dust sucking valve 44 is closably provided to a dust sucking cylinder 43 which is opened to a dust sucking duct side. Further an auxiliary suction valve 46 is closably provided to an auxiliary suction port 45 for sucking the atmosphere which is formed to the side wall of the suction collecting chamber 23. An interlocking means 47 for opening, closing and actuating these valves 42, 44 and 46 is operated by a valve opening and closing means 49 with a timer 48 equipped thereto. In order words, the valves 42, 44 are closed and the valve 46 is opened at the initial stage of polishing work and when prescribed time elapses, the valve 46 is closed and the valves 42, 44 are opened. As a result, effective polishing work can be performed.
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