Patent ID: 6988381

Claim:
A method of elongating a glass preform, comprising: holding both ends of a glass preform having holes extending in the longitudinal direction by a first holding member and a second holding member, respectively; and successively heat-melting the glass preform from an end thereof by a heating means while increasing the distance between the first holding member and the second holding member in the longitudinal direction of the glass preform so as to elongate the glass preform; wherein the glass preform is elongated by heat-melting with the heating means so that the temperature T satisfies a relation by Eq. 1 11[° C./mm]· D [mm]+860[° C.]< T [° C.]<17[° C./mm]· D [mm]+880[° C.] (1) where D is the outer diameter of a post-elongation glass preform, and T is the maximum temperature of a softened portion of the glass preform (prre-elongation) heat-melted by the heating means.