A press mold for glass substrate includes an upper mold and a lower mold, and a pressure apparatus for applying pressure to the upper mold and the lower mold, for molding a plate-shaped glass substrate having a predetermined thickness between the upper mold and the lower mold. An engaging projected piece is projectingly provided on the side portion of the upper mold, an engaging projected piece supporting portion for supporting the engaging projected piece is provided on the side portion of the lower mold, and an end portion of the upper mold is formed so as to be released from the lower mold with the engaging projected piece as a rotating shaft. Variance in pressure on mold surfaces between the upper mold and lower mold is detected, and a buffer made of material having lower compressive yield strength than material constituting the lower mold is inserted between the lower mold and the pressure apparatus in a position corresponding to the mold surface portion at lower pressure. It is possible to prevent the molded object or the mold from being damaged, and to apply uniform pressure on an entire mold surface by eliminating pressure variance on the mold surface of the mold as far as possible, and therefore, a large glass substrate molded object of excellent quality can be molded.