A metal bond grinding wheel 12 having a horizontal working surface 12a, a holding and rotating means 14 for a workpiece having a horizontal supporting surface 14a opposite to said working surface 12a, a voltage applying means 16 having the metal bond grinding wheels and an electrode 16a installed oppositely to the working surfaces in an uncontacted state and applying a pulsed voltage between them, a grinding fluid feeding means 18 for feeding an electroconductive grinding fluid to the working surfaces are installed. The holding and rotating means 14 holds and rotate a disk-like magnetic disc substrate 1 or a truing grinding wheel 2 to closely contact to its supporting surface, has constitution capable of moving horizontally and vertically, wherein a surface for working 12a is processed to yield a flat surface on the machine, subsequently, alternative operations on the machine are carried out for grinding of the supporting surface 14a of the holding and rotating means of the workpiece simultaneously with electrolytic dressing of the metal bond grinding wheel and grinding of the magnetic disc substrate 1 attached to the holding and rotating means of the workpiece.