There are methods for manufacturing glass plates by employing down-draw process, as disclosed in Patent Literature 1 (Japanese Patent Application Laid-Open Publication JP-A-2004-115357). In down-draw process, molten glass is first poured into a forming member, and then the molten glass is made to overflow from the top sections of the forming member. The molten glass that has overflowed then flows downward along the opposite side surfaces of the forming member, and the streams of molten glass merge at the lower end of the forming member, thus being made into a sheet-form glass (sheet glass). The sheet glass is then drawn downward by rollers and cut into predetermined lengths.