PURPOSE: To greatly enhance the abrasion resistance by fixing a hard material mainly containing diamond in part of at least two mating surfaces of the inner side-face of the opening of a grinding wheel holder.

CONSTITUTION: The body 1 of a grinding wheel holder is provided with an opening 1a having a quadriangular section perpendicular to the grinding wheel inserting direction. A hard material chiefly containing diamond 2 is fixed to a part of at least two mating surfaces of the inner side-face of this opening 1a. Examples of this hard material are a synthesized monocrystal diamond, sintered diamond, and ceramic covered with polycrystal diamond by the low pressure gaseous phase method and a single substance of plate-shaped polycrystal diamond synthesized by the low pressure gaseous phase method.