PURPOSE: To promote drying of abrasive material immediately after cleaning by adding volatile substance to a liquid cleaner used to clean the abrasive material.

CONSTITUTION: In polishing pachinko balls in a polishing device 1, contaminated abrasive material on the surfaces passes through an abrasive material circulation path 8 and part of it is led to a detour 12 and introduced into a cleaning tank 13 to be agitated and cleaned by an agitation impeller 17 while a liquid detergent with volatile substance added to is poured in. The abrasive material having got rid of contaminations is sent to a tubing 18 from the bottom of the cleaning tank 13, rises within the tubing with rotation of a spiral 20, and from the top of this tubing, passes through a return path 21 to diverge at the abovementioned abrasive material circulation path 8. At this time, the volatile substance moisten the surface of the abrasive material, which is therefore dried quickly to provide good slide with each other, and thus smooth transport is accomplished.