One aspect is a process to producing a synthetic quartz glass, including an annealing treatment that includes: putting a synthetic quartz glass as a parent material into a heat treatment furnace; elevating a temperature in the heat treatment furnace to a prescribed keeping temperature that is equal to or higher than the annealing point; keeping the keeping temperature; annealing the synthetic quartz glass; and taking the synthetic quartz glass out of the heat treatment furnace. The process includes determining an annealing rate v [° C./h] of the annealing step based on a value of S/V [mm2/mm3], wherein S [mm2] is the surface area of the synthetic quartz glass as a parent material and V [mm3] is the volume thereof and a target birefringence Re [nm/cm] for the synthetic quartz glass after the annealing, and the annealing step is performed at the determined annealing rate v.