To prevent dropping off of abrasive particles and keep the shape of a blade in a stable condition for a long time by forming a tool material by polycrystalline diamond sintered body.

A tool material 10 is composed of a support layer 11 made of cemented carbide (tungsten carbide) and a polycrystalline diamond sintered body (PCD) layer 12 formed on the support layer 11. The tool material 10 is manufactured by overlapping powders of tungsten carbide and minute diamond crystalline particles in which a small amount of cobalt is mixed and sintering them under high pressure at high temperature. Next, the tool material 10 is set to a wire cut electric discharge machine to manufacture a grinding wheel material having the required thickness by wire cut-electrical discharge machining the PCD layer 12 in an insulation liquid by using a wire and the PCD layer 12 as electrodes. Consequently, it is possible to prevent dropping off and wear of abrasive particles and machine even a groove having a sharp angle like a square or V-shaped groove with high precision.