PURPOSE:To prevent the generation of bubbles during drawing by forming internal burr on the interface between quartz rods of a small diameter with a gas reactive at a low temp. CONSTITUTION:A quartz pipe 2 of a large diameter contg. a plurality of arranged quartz rods 1 of a small diameter for image elements is attached to a glass lathe 3 before drawing, and a prescribed gas 5 reactive at a low temp. is fed into the pipe 2 while heating the rods 1 and the pipe 2 with an oxyhydrogen burner 4. A reaction product of the gas 5 having the same composition as the clads 6 is formed on the interface between the rods 1 and the inside of the pipe 2 as internal burr 7.