PURPOSE: To purity the surface of an abrasive material on the way of circulation of the abrasive material and to allow it to circulate again by allowing a lead-out gutter of the abrasive material ejected from a small ejection hole to communicate with an abrasive material purifier provided adjacently to a grinding machine main body, and allowing a lead-in gutter of the abrasive material purified with the abrasive material purifier and the emission gutter of a hopper where a soiled medal is thrown to communicate with the inside of a cover.

CONSTITUTION: When the soiled medal and the abrasive material are thrown into the grinding machine main body (a), and a motor 10 is riven, a screw 6 rotates and the medal and the abrasive material are transferred successively to the upper part, while being stirred, ejected between a cover 4 and an inner cylinder 5 from the ejection port 13 of the peripheral surface of the upper end part of the inner cylinder 5, and during this time, contamination of the medal is ground by the abrasive material. The medal and the abrasive material are separated by a separating mechanism 14, the medal is fed to a carry-out gutter 15, and the abrasive material is allowed to circulate into the inner cylinder 5 from a circulation port 16 from an inclined guide plate 17. Also, in the course of stirring and grinding, a part of a soiled abrasive material is ejected from a small ejection hole provided on the inner cylinder 5. When the surface of the abrasive material is soiled remarkably and an abrasive material purifying device (b) is driven, a soiled abrasive material which fills the inside of a lead-out gutter 19 and a soiled abrasive material ejected successively from the small ejection port are purified by the abrasive material purifier (b) and pass through a lead-in gutter and allowed to circulate to the guiding machine main body (a).