Provided is a method for manufacturing sheet glass by float shaping. In this method, a shaping zone (F1) of a glass ribbon (4) is partitioned, on the basis of the viscosity distribution of molten glass (3), into an upstream row, a middle row and a downstream row in the flow direction of the molten glass (3) and, in at least the upstream row and the downstream row, into a central portion and two side portions in the width direction of the glass ribbon. In the steady state of the flow of the molten glass (3), the outputs of heaters (11) of both the section (a1) of the central portion of the upstream row and the section (c1) of the central portion of the downstream row of the shaping zone (F1) of the glass ribbon (4) are cut, and the upper space (17) of a ceiling wall (7) is partitioned to correspond to the section of the shaping zone (F1) of the glass ribbon (4). The flow rate per unit area of the gas to flow into a bath inside (18) from the regions (A1 and C1) of the upper space (17) corresponding to at least either of the section (a1) of the central portion of the upstream row or the section (c1) of the central portion of the downstream row is controlled for the gas flow rates perunit area of the regions of the two side portions.