A diamond tool is combined with a processing apparatus to process a workpiece. The diamond tool includes a shank, a segment, and an abrasion preventing part. The shank has a throughhole through which grinding powder generated during processing the workpiece by the processing apparatus is discharged outside. The segment is bonded to an end portion of the shank. The segment contacts and processes the workpiece. The abrasion preventing part is disposed on an adjacent portion among an outer surface of the shank adjacent to the throughhole to prevent abrasion of the outer surface during the processing of the workpiece.