Abstract: A cup grinding wheel 20 which is mounted on a rotating tool 10 and rotates to grind a surface of a physical object is formed of a central base member 21a approximately shaped like a circular disc having a mounting hole 22a at a center thereof, an exterior base member 21b, a grinding portion 27 and a screw member 29. The exterior base member 21b is formed of a rim engaging portion 25 which can be engaged with an outer circumferential portion of the central base member 21a, and a flanged rim fastening portion 26 provided on a front rim of the rim engaging portion 25. Furthermore, the grinding portion 27 is fixed to the front of the rim fastening portion 26 of the exterior base member 21b with the screw member 29.