A method of manufacturing a glass sheet includes creating split flows of molten glass in a forming body (10) and causing the molten glass to flow down, subsequently merging the flows at a merging point to form a glass sheet G and causing the glass sheet to flow downward in the vertical direction. A plurality of chambers (42b, 42c, . . . ) separated by heat-insulating plates (40a, 40b, . . . ) in the direction of movement of the glass sheet G are provided. A heater (60a, 60b, . . . ) is provided for each of the chambers (42b, 42c, . . . ) so that the temperature decreases in the direction of movement. The heat-insulating plates (40a, 40b, . . . ) are disposed facing the glass sheet G, and facing surfaces of the heat-insulating plates (40a, 40b, . . . ) are shaped so as to correspond to a sheet thickness variation of the glass sheet G.