To eliminate problems of a conventional face reduction processing process such as material cutting and shaving, grinding, extrusion, etc., in which an oil and fat-based lubricant has characteristic difficulty in handling, a lubricant has difficulty in removal after use, waste liquor treatment after the removal and a high cost, especially the oil and fat-based lubricant or the like require a number of measures in terms of environmental protection and economic efficiency.

In processing a material having form change ability in grinding or a face reduction processing into various shapes, an oil and fat-based lubricant is not used on the surface of a material as it has been used conventionally and a suspension of maize flour, rice flour, soybean flour or the like mainly consisting of carbohydrates, and protein components in water is sprayed or directly applied to the surface instead of the oil and fat-based lubricant to carry out the face reduction processing such as cutting and shaving, grinding, extrusion or the like. Consequently, labor for waste oil treatment in a conventional processing process is eliminated and a processed product having excellent surface properties is obtained.