A method of producing a glass having a SiO2—Al2O3—B2O3—RO based composition, where RO is at least one of MgO, CaO, BaO, SrO and ZnO, a melting temperature corresponding to 102.5 poise of 1570° C. or higher and an alkali content of 0.01 to 0.2% and a ZrO2 content of 0.01 to 0.3%, as expressed in % by mass. And, a method of producing a glass having a SiO2—Al2O3—B2O3- RO based composition, where RO is at least one of MgO, CaO, BaO, SrO and ZnO, a density of 2.5 g/cm3 or less, an average thermal expansion coefficient of 25 to 36×10−7/° C. in a temperature range of 30 to 380° C., a strain point of 640° C. or higher and an alkali content of 0.01 to 0.2% and a ZrO2 content of not less than 0.01% and less than 0.4%, as expressed in % by mass.