Fabrication method for porous glass base material for optical fiber

A fabrication method for a porous glass base material for optical fiber, comprising:

• supplying a glass raw material gas to a burner via a mass flow controller;
• generating glass fine particles in flame formed by ejecting the glass raw material gas and a combustible gas from the burner;
• and
• depositing the glass fine particles on a rotating starting material,
• wherein the burner continuously ejects inert gas having passed through the mass flow controller for at least a predetermined period immediately after an end of deposition of the glass fine particles,
• wherein the inert gas at 10% or less of a maximum value of a mass flow rate range is caused to continuously flow into the mass flow controller for at least the predetermined period immediately after the end of the deposition of the glass fine particles, and
• wherein an additional inert gas is introduced from downstream of the mass flow controller to control a linear speed of the inert gas at a burner outlet.