Optical fiber preform manufacturing method for shrinkage and closing of deposited tube

An optical fiber preform manufacturing method whereby a clad layer and core layer are deposited on the inner surface of a preform tube for forming a deposited tube. One end of the deposited tube is shrunk and closed. The deposited tube which has a closed end is arranged extending vertically through a circular heater. A heat is applied to the deposited tube at a temperature lower than the softening point of a deposited tube, exhausting contaminants existing in the interior of the deposited tube while moving the circular heater. The heating temperature of the circular heater is then set to a temperature not lower than the softening point of the deposited tube-to shrink and close the deposited tube.