METHOD FOR PRODUCING GLASS PREFORM

PROBLEM TO BE SOLVED: To provide a method for producing glass preform, which can prevent intrusion of impurities from outside and surely prevent the inside of a furnace core pipe from being contaminated when not in operation.SOLUTION: There is provided the method for producing glass preform in which a glass microparticle deposition 13 deposited of glass microparticles is suspended in the furnace core pipe 11 and the glass microparticle deposition 13 is heated from outside of the furnace core pipe 11 for dehydrating and sintering it. When not in operation other than in dehydration and sintering, standby temperature in the furnace core pipe 11 is maintained at 700°C or above for preventing the intrusion of the impurities.