Method of manufacturing glass substrate for magnetic disk, method of manufacturing magnetic disk, and polishing apparatus of glass substrate for magnetic disk

A method of manufacturing a glass substrate for a magnetic disk, including an inner circumference polishing step of polishing an inner circumferential end face of a cylindrical polishing object including a plurality of disk-like glass substrates stacked on one another, each of the disk-like glass substrates having an inner hole formed in its center, wherein:

• a polishing member, which has a rotation axis and polishing parts provided around the rotation axis, is inserted into an inner hole of the polishing object,
• then the polishing parts are expanded in a direction perpendicular to the rotation axis of the polishing member, thereby the polishing parts are elastically pressed to the inner circumferential end face of the polishing object at even pressing force and are contacted in face contact to the inner circumferential end face of the polishing object,
• the polishing parts comprise grinding stones, respectively, and a liquid coolant is supplied between the grinding stones and the inner circumferential end faces of said plurality of disk-like glass substrates, and
• then, while the center of the inner hole of each of the disk-like glass substrates and the rotation axis of the polishing member correspond during polishing and while the polishing parts are simultaneously in face contact of 50% or more with the inner circumferential end face of the polishing object during polishing, at least one of the polishing object and the polishing member is relatively moved, thereby the inner circumferential end faces of said plurality of disk-like glass substrates are mirror-polished.