To keep flatness of a glass substrate surface, to remedy roughness of the glass substrate surface, and to remove defect on the glass substrate surface, in a polishing process of polishing the locally-worked glass substrate surface for remedying the roughness by the local working and removing the defect.

This manufacturing method of a glass substrate for mask blanks comprises: an uneven shape measuring process of measuring unevenness on the glass substrate surface; a flatness controlling process of controlling the flatness on the glass substrate surface to a predetermined reference value or lower by applying the local working based on the measured result obtained in the uneven shape measuring process; and a non-contact polishing process of polishing the glass substrate surface applied with the local working, by an action of the working fluid interposed between the glass substrate surface and a tool surface for polishing, and without contacting with the tool surface for polishing, after the flatness controlling process.