PURPOSE: To enable to regulate the cutting amount in accordance with the abrasion of a dresser by a method wherein the relationship between dressing resistance and the flexure of a wheel spindle is previously stored in a memory, the dressing resistance is detected and the dressing is conducted while extending and contracting a magnetostrictive element in accordance with the flexure of the spindle.

CONSTITUTION: When the grinding wheel 11 contacts with the dresser 12, the state of abrasion of the bresser and the amount of the resulting flexure of the wheel spindle 11a are estimated from a previously empirically obtained curve based on the dressing resistance and is fed to an amplifier 22 throuth a dressing resistance measuring device 17 and a calculator 20. On the other hand, in accordance with the change of the position of the wheel 11 in the axial direction relative to the dresser 12, a reference voltage corresponding to the flexure of the wheel spindle 11a is fed to the amplifier 22 from a reference voltage generator 12 at a predetermined timing. As a result, the amplifier 22 impresses on a coil 14 the voltage obtained by multiplying the mu-factor, which corresponds only to the state of abrasion of the dresser and is fed fromthe calculator 20, with the factor corresponding only to the position of the wheel in the axial direction and being fed from the voltage generator 21. By this, the magnetostrictive element 13 is expanded to cause the dresser 12 to cut into the grinding wheel 11 for dressing the latter.