Manufacturing method of optical fiber preform

A manufacturing method of an optical fiber preform used to produce an optical fiber, the optical fiber including a core that is formed of silica glass and a cladding that is formed around an outer circumference of the core, the manufacturing method comprising:

• etching a surface of a core preform that forms the core with a plasma flame in a chamber;
• obtaining a porous preform by depositing glass particles on an etched surface of the core preform to form an outside vapor-deposited layer that forms the cladding in a state where the core preform is put into the chamber;
• and
• heating and sintering the porous preform, wherein
• when obtaining the porous preform, the outside vapor-deposited layer is formed by repeating the deposition of the glass particles multiple times through supply of source material gas,
• in a first deposition among the multiple times of deposition of the glass particles, a flow rate of the source material gas is less than or equal to 50% of a stable value,
• the flow rate of the source material is increased to the stable value in a number of depositions that corresponds to less than or equal to 21% of all the multiple times of deposition, and
• a temperature of the etched surface of the core preform at a start of depositing glass particles is greater than or equal to 50° C.