The invention provides a method for manufacturing a glass substrate and a device for manufacturing glass substrate. The method for manufacturing a glass substrate, including: a step for melting a raw glass material in order to form glass that includes tin oxide and is difficult to melt, by combustion heating in a gas phase by a combustion means and joule heating by causing a current to flow in molten glass, within a melting pot; and a clarifying step for clarifying the molten glass by a redox reaction of the tin oxide. The combustion heating and the joule heating are performed such that a heat ratio of heat from the combustion heating to heat from the joule heating is 1.0 to 3.4. When making molten glass to become glass that has a viscosity of 102.5 poise at a temperature of 1580 DEG C or greater, the heat ratio is 1.0 to 2.8.