PURPOSE: To facilitate forming with high efficiency and accuracy by employing a diamond grinding wheel where diamonds are bonded through conductive binder and a grinding wheel where hard abrasive grains are bonded through conductive binder, then applying electrical discharging waveform between both grinding wheels and combining thermal functions.

CONSTITUTION: A diamond grinding wheel 1 where diamonds are bonded through metal bond is fixed to a grinding wheel shaft 5 and rotated, while a metal bond diamond grinding wheel is employed as a forming grinding wheel 6 and rotated. They are set such that the outer circumferential face of the forming grinding wheel 6 contacts with the forming face 2 of the diamond grinding wheel with an angle of 45°, then predetermined cutting quantity is provided and the forming grinding wheel 6 is moved by a slide table 8 so as to machine the forming face 2, thereafter the forming face 3 is formed similarly. Here, the diamond grinding wheel 1 and the forming grinding wheel 6 are connected respectively with + and - electrodes through an electrical discharge machining power source 11 so as to combine electrical discharge machining functions. Since a portion of binder in the diamond grinding wheel 1 is fused and removed and holding force is weakened, falling of abrasive grains from the surface of the diamond grinding wheel 1 is promoted by the abrasive grains in the forming grinding wheel, resulting in facilitation of forming.