PURPOSE: To enable production of a special grinding wheel having different diameters by providing the rotatable special grinding wheel having different diameters, a transferring body for a round bar to be ground, and a positioning disc for the round bar.

CONSTITUTION: A general grinding wheel 5 whose width is equal to the radius of rotation of the tool edge of a grinding wheel forming device 6, and the rotary grinding wheel forming device 6 which has a shaft at a position perpendicular to the center line 7 of a grinding wheel 5, and a diamond tool edge having its lowest point positioned coinciding with the extension line 8 of a horizontal line passing through the center of the front face of the grinding wheel are provided to produce a special grinding wheel having different diameters. In addition to that, a transferring body 3 to transfer a round bar 2 arcuately in the direction rectangular to the central axis of the round bar 2 as the round bar 2 is rotated centering around the central axis of the round bar 2 to be ground, and a round bar positioning device 4 to slowly shift the grinding position of the end part of the round bar 2 are provided.