A support glass substrate of the present invention is a support glass substrate for supporting a substrate to be processed, the support glass substrate including, as a glass composition, in terms of mol %, 50% to 80% of SiO2, 0% to 25% of Al2O3, 5.5% to 20% of B2O3, 0% to 5% of Li2O+Na2O+K2O, 0% to 15% of MgO, 1% to 25% of CaO, 0% to 10% of SrO, and 0% to 10% of BaO, having a molar ratio (MgO+SrO+BaO)/CaO of 1.5 or less, and having an average coefficient of thermal expansion at from 30° C. to 380° C. of from 35×10−7/° C. to 60×10−7/° C.