PURPOSE: To allow inexpensive mass production with high quality at a high yield by heating a porous quartz glass base material in a 1st gaseous atmosphere having the coefft. of diffusion, etc., larger than the coefft. of diffusion, etc., in quartz glass to form a transparent glass rod, then subjecting the rod to a specific heat treatment.

CONSTITUTION: While the porous quartz glass base material 1 having about 150mm diameter and about 600mm length is rotated in a zone heating furnace 4 of a reaction vessel 3 of 1atom, etc., of the atmosphere consisting of He, the base material is lowered at about 10mm/min and is heated for about 150 minutes at about 1600°C to obtain the transparent glass rod. The atmosphere in the heating furnace 4 is then replaced sufficiently with N2, etc., having the coefft. of diffusion and solubility in the quartz glass sufficiently smaller than the coefft. of diffusion and solubility of the above-mentioned He, etc., while the rod is held inserted into the furnace; thereafter, the rod is heated to about 1500°C. The rod is moved upward at about 10mm/min under heating and is heat-treated for about 120 minutes, by which the high-purity quartz glass is produced.