PURPOSE: To operate polishing with stability and high precision, by controlling so that the loads of a motor which turns the grindstone, a motor which feeds the work, a motor which feeds cuts and a motor which moves the work in the direction of axis Y are made constant.

CONSTITUTION: Work 6 mounted on processing table 5 is ground by grindstone 11. Motor 7, which gives a required cut on work 6, detect and discriminates (11) the load current of motor 3 of grindingwheel 2 and is controlled by device 12. Motor 3, which feeds cuts to grindingwheel 1, and motor 8, which gives table 5 a slide in the direction of axis Z are automatically controlled by NC control device 9, and thereby work 6 is ground under a constant load at all times.