PURPOSE: To improve the efficiency of grinding processing by performing it by prescribed times at the 1/3W1/2 cutting speed of a usual one without performing dressing a CBN whetstone after truing it and thereafter grinding a workpiece under a normal condition.

CONSTITUTION: When a CBN whetstone grinds a workpiece under a normal condition without dressing the whetstone after tooling it, the surface of the whetstone welds resulting in the deterioration of processing quality, but when performing grinding reducing the cutting speed to 1/3W1/2, no deterioration of the quality is produced. In case workpieces of high-carbon chrome steel are subjected to infield grinding with the CBN whetstone, two workpieces are ground by reducing the cutting speed from 1.1 to 0.6mm/min in 3x and from 0.3 to 0.16mm in 4x. From the third workpiece the cutting quality of the whetstone is also recovered, enabling processing with a normal cutting speed.