A glass ball has a density of 2.3 to 3.2 g/cm3, a Young's modulus of 60 to 150 GPa, and an average coefficient of thermal expansion at 50 to 350° C. being 40×10−7 to 120×10−7/° C. The glass ball is formed of a glass material including, as represented by mole percentage based on oxides, 30 to 75 mol % of SiO2, 2 to 30 mol % of Al2O3, and 5 to 25 mol % of R2O, where R is at least one kind selected from Li, Na and K. The glass ball includes a compressive stress layer in a surface thereof.