PURPOSE: To make it possible to perform minute feed of a spindle at a low cost and compactly by positioning the spindle between a rotary fulcrum and a driving section and by converting vertical motion of this driving section to the minute rotary motion centering the rotary fulcrum.

CONSTITUTION: Rotation of a ball screw 10 makes a nut 11 move vertically. The vertical and linear motion of this nut 11 is converted to the minute rotary motion of a holder 18 for holding a diamond driving spindle centering a pin (rotary fulcrum) 16 by a cam follower 15. As a result, the spindle held by the holder 18 is fed minutely grinding and forming a groove of a predetermined depth on a semiconductor wafer by the diamond wheel held by this spindle.