A method of manufacturing a glass blank for a substrate for an information recording medium, the method including steps of: cutting out a gob of a glass material from a molten glass material by cutting the molten glass material discharged from a glass material outlet at a predetermined timing; causing the gob of the glass material to fall downwardly; pinching and pressing the gob of the glass material by a press unit having a pair of molds, the molds' surfaces facing to each other being press surfaces which are planes without an unevenness, so as to contact the falling gob of the glass material only to the press surfaces; and forming a circular flat plate-shaped glass blank having a target flatness as a glass substrate for a magnetic disk such that a ratio between a diameter and a thickness of the glass blank is within a range of from 50:1 to 150:1, from the gob of the glass material.