Provided is a method of manufacturing an optical fiber preform, comprising obtaining a base material ingot by sintering a porous glass base material at a high temperature to change the porous glass base material into glass while retaining an unsintered portion at one end thereof that is not completely changed to glass; and while relatively moving a heating means in a longitudinal direction of the base material ingot, applying a tensile force to a heated portion and beginning to extend the unsintered portion from one side to decrease a diameter of and extend the base material ingot.