PURPOSE: To enable the automatic setting of the optimum oscillating angle in accordance with a machining condition by providing an operating portion for measuring the distance between a workpiece installing portion and a grinding wheel and for operating the difference between the oscillating angle obtained from the measured value and a set value, and a driving portion for adjusting the oscillating angle of a wheel spindle according to the error signal, or the difference.

CONSTITUTION: The distance between a flat plate 4 provided on a workpiece installing portion and the circumference of a grinding wheel 1 is measured by set-up sensors 9 at two or more points. The oscillating angle θ of a wheel spindle 2 is calculated by an operating portion based on the data measured by the sensor 9, to obtain the difference between this oscillating angle and a previously set set value, i.e., an error signal. Based on this error signal, a θ-axis motor 13 is controlled in its driving and a desired angle θ-axis driving portion is operated to adjust the oscillating angle of the wheel spindle to the optimum oscillating angle with respect to the machining condition.