To provide a fixed grinding stone without possibilities of oblique cracking due to fastening force on fixing through a support and cracking in the circumferencial direction due to rotation stress acting for a long period.

The engagement face 2b of the fixed grinding stone 2 extends obliquely and linearly from the peripheral surface 2e. An annular side surface 23a and a kick-out annular portion 23b are formed inside a support 23 of the body 9 of an upper lid, on which an annular member 24 is mounted. The annular member 24 has an inner peripheral surface 24c in tight contact with the level-less engagement face 2b. When a bolt 8 to be inserted through the upper lid 7 is screwed into the support 23 and fastened, the fastening force of the bolt 8 is transmitted from the kick-out annular portion 23b to the annular member 24 and then from the inner peripheral 24c to the reversed-truncated-cone-like engagement face 2b of the fixed grinding stone 2. Although the load acts in the peripheral direction of the level-less engagement face 2b and in the direction perpendicular to the peripheral direction, there occurs little oblique tensile force possibly producing oblique cracking and no cracking in the circumferential direction.