PURPOSE: To enhance the reaction efficiency of gaseous starting materials by simple construction by putting a central rod in a rotary glass tube into which the gaseous materials are blown in an apparatus applying a CVD method and using a moving heating source.

CONSTITUTION: An oxyhydrogen burner 3 is moved along the longitudinal direction of a transparent glass tube 1 with a circular cross section attached to a rotating and supporting mechanism 2. A central rod 22 reducing the hollow cross section of the tube 1 is put in the tube 1 from the discharge side edge 21 of the tube 1 in the longitudinal direction. The preferred material of the rod 22 is high purity quartz, and the suitable outside diameter is about 70% of the inside diameter of the tube 1. In order to prevent the heating temp. of the hollow central part of the tube 1 from being mede lower than the temp. of the wall and fine glass powder from depositing on the outside of the rod 22, the rod 22 is internally provided with a heater 23. By depositing and melting a glass product by a CVD method while rotating the tube 1, gaseous starting materials introduced into the tube 1 flow through a region almost equal to the wall in temp., and the reaction efficiency forming the glass product 4 is enhanced.