PURPOSE: To make it possible efficiently and satisfactorily grind a workpiece, by selecting an ATF speed, a main drive speed and a wire feed speed for a wire saw in accordance with the cross-sectioned shape of the workpiece.

CONSTITUTION: Given conditions corresponding to the shape of a workpiece 15 are inputted to a control starting condition judging means through keyboard operation of a control type selection input means, and those to be controlled are selected among drive means 33, 43, 42 for ATF, main drive and wire feed, respectively, while a switch is changed over between a manual mode and an automatic operation mode. Further, when the judging means determines that the preparation of start of a wire saw is completed in accordance with a signal from a sensor 37, a control signal setting means receives a control function, its parameters and the like from the input means, and therefore the feed speed of a table 4, the main drive speed and the feed speed of a wire 18 are controlled by means of the switch while a control signal correcting means receives feed- back signals from weight and load detectors 31, 36. Thus, it is possible to efficiently and satisfactorily perform a grinding process and to reduce the consumption of the wire.