PURPOSE: To prevent thermal expansion of a wear resistant layer on the inner wall of a polishing vessel, leakage or stagnation of polished dust and mud or polished works or abrasive materials in a gap between a pedestal and a rotary disc to maintain the rotation of the rotary disc favorably, remove polished dust in the polishing vessel quickly, and prevent the polished dust from scattering outside the machine body.

CONSTITUTION: A clearance between a pedestal 4 and a rotary disc 2 is connected through air pipes 12a, 12b to a compressed air supply source or a compressor 13, and a fine clearance 10 is provided between a wear resistant layer 2a of the rotary disc 2 and an inner wall-wear resistant layer 1a of the outside 1 of a polishing vessel. The upper part of the polishing vessel is covered and closed with a polishing vessel cover 3 provided with an exhaust hole 3a, an exhaust pipe 3b in its center part so that the cover can be freely loaded and removed. The exhaust pipe 3b is connected to a dust collector 18.