Method of manufacturing optical fiber preform

A method of manufacturing an optical fiber preform, comprising the steps of:

• disposing a rod member made of a silica-based material within a cavity of a mold, followed by loading a molding material within the mold cavity;
• pressurizing the mold from outside of the mold to form a porous layer on the surface of the rod member and, thus, to obtain a porous preform;
• wherein at least one end portion of the rod member extends outside the mold cavity in the step of pressurizing the mold;
• attaching a supporting member larger in diameter than the rod member to at least one end of the rod member, the supporting member and the rod member each having a respective cross sectional area;
• and
• setting a molding pressure P in said pressurizing step to meet formula (I) given below:
• P/(A/B)<4000 . . . (I)
• where A is the cross sectional area of the rod member, and B is the cross sectional area of the supporting member.