PURPOSE: To prevent the reduction of grinding allowance by securing elastic grinding wheels to a rotary shaft inclined and with the outer circumferential surfaces of the grinding wheels parallel with the shaft center of the rotary shaft, and establishing a specified relationship among the inclination angle, the width in the direction of the grinding wheels and the shaft center, and the diameter of the grinding wheels in a mounted state.

CONSTITUTION: A plurality of grinding wheels 10 are attached to a rotary shaft 2 at an angle of θ to the perpendicular plane to the shaft center of the rotary shaft 2. In addition, the outer circumferential surfaces of the elastic grinding wheels (hereinafter referred to grinding wheels) 10 are set to be parallel with the shaft center of the rotary shaft 2. Spacers 20 are provided among the grinding wheels 10. The relationship of θ≥max {arctan (A/D), arctan (B/D)} is set among the inclination angle θ, the width A in the direction of the shaft center of the grinding wheels 10, the width B in the direction of the shaft center of the spacer 20, and the diameter D the grinding wheels in a mounted state.