To provide a method and device for grinding a flap wheel that can manage grinding work and set the hardness of the surface of a body to be ground to prescribed hardness or lower.

The flap wheel grinding method rotates a flap wheel 9 which is formed by radially installing a large number of rectangular flaps 11 at the circumference of a rotating shaft 5 and formed into a cylindrical shape, and grinds the body to be ground by making it abut on the circumference of the flap wheel 9. A relationship between and among the rigidity of the flap wheel 9, a pressing force to the body to be ground of the flap wheel 9 and the hardness of the surface of the body to be ground are acquired in advance, and the flap wheel is ground by managing the rigidity and the pressure force of the flap wheel 9 so that the hardness of the surface of the body to be ground may be lowered to the prescribed hardness or lower on the basis of the acquired results.