PURPOSE: To provide a resinoid grindstone having an excellent grinding characteristic, by combining an abrasive material with a filler of styrofoams from which voltatile components are partly removed so that the styrofoams have a desired particle size.

CONSTITUTION: Pores having a substantially equal diameter are formed in a grindstone by containing therein styrofoams from which volatile components are partly removed by heating them so that they have a substantially equal particle size, thereby the grinding characteristic of the grindstone is improved. For example, the material which is made by mixing the thus treated styrofoam material into a compound of 89.50% artificial grinding agent, WA#60, 8.0% powder resin for grindstone and 2.5% liquid resin for grindstone, is charged into a die and then is formed under cold compression. Thereby, a desired grinding characteristic may be obtained by thus produced resinoid grindstone.