Process for production of glass preform for optical fiber and apparatus for the same

A process for the production of a porous glass preform for an optical fiber and an apparatus for such a process are provided. In the process, fine glass particles are produced by heating and reacting vaporous starting materials for glass in a reaction vessel, the thus produced fine glass particles are deposited to obtain the porous glass preform and an exhaust gas speed through an exhaust duct which exhausts an exhaust gas containing non-deposited fine glass particles from the reaction vessel is controlled to be above 15 m/sec. Preferably, pressure fluctuation in the reaction vessel is minimized by supplying air from the outside of the reaction vessel to the exhaust duct. According to the present invention, the exhaust duct is not likely to be blocked by the non-deposited fine glass particles so that the stable production of the preform is maintained over an extended period.