A tapered cutting edge portion (4) and a continuous raise portion (6) from the tapered cutting edge portion (4) are ground in an edge portion of a straight grinding raw material so that an eccentricity is not generated. In a method for grinding a treatment device (1), one end portion of a tapered grinding raw material (4) is inserted between a grinding surface (13a) of a grindstone (13) and a pressing surface (14a) of a press block (14), and finishing surfaces opposite each other while having a predetermined dimension, shape, and angle are ground so that a direction in which abrasive grains of the grindstone (13) run corresponds to a direction of a shaft center. At this point, before the finishing surfaces are ground in the predetermined dimension, shape, and angle which are previously set corresponding to an objective reamer (A), pre-grinding is performed while a necessary finishing margin with respect to at least one of the surfaces, and then finishing grinding is performed to the other surface.
