To provide a polishing device capable of removing a processing distortion existing on a back surface of a semiconductor wafer by polishing the back surface thereof with a high polishing efficiency and a high polishing quality and a grinding/polishing machine to which the polishing device is assembled.

The polishing device 66 is provided with a chuck means 44; and a polishing tool 2. The polishing tool has a polishing means 6 constituted by dispersing an abrasive grain in a felt of which a density is 0.20 g/cm3 or more and a hardness is 30 or more. The substance to be processed is polished by rotating the chuck means and the polishing tool and pressing the polishing means of the polishing tool to the substance to be processed retained by the chuck means.