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: an etching step of etching a surface of a core preform that forms the core with a plasma flame in a chamber ; a deposition step of 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 a sintering step of heating and sintering the porous preform, characterized in that : in the deposition step, the outside vapor-deposited layer is formed by repeatedly performing the deposition of the glass particles multiple times through supply of source material gas, in at least a first deposition among the multiple times of deposition of the glass particles, a flow rate of the source material gas is 50% or lower with respect to a stable value (S1), the stable value (S1) that ranges from 90% or higher to 100% or less with respect to a maximum flow rate (M1) of the silica glass source material gas, a flow rate of the silica glass source material gas in a final deposition among the multiple times of deposition of the glass particles is the maximum flow rate (M1) of the silica glass source material gas, and a temperature of the etched surface of the core preform at a start of the deposition step is 50°C or higher. an etching step of etching a surface of a core preform that forms the core with a plasma flame in a chamber ; a deposition step of 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 a sintering step of heating and sintering the porous preform, characterized in that : in the deposition step, the outside vapor-deposited layer is formed by repeatedly performing the deposition of the glass particles multiple times through supply of source material gas, in at least a first deposition among the multiple times of deposition of the glass particles, a flow rate of the source material gas is 50% or lower with respect to a stable value (S1), the stable value (S1) that ranges from 90% or higher to 100% or less with respect to a maximum flow rate (M1) of the silica glass source material gas, a flow rate of the silica glass source material gas in a final deposition among the multiple times of deposition of the glass particles is the maximum flow rate (M1) of the silica glass source material gas, and a temperature of the etched surface of the core preform at a start of the deposition step is 50°C or higher. in the deposition step, the outside vapor-deposited layer is formed by repeatedly performing the deposition of the glass particles multiple times through supply of source material gas, in at least a first deposition among the multiple times of deposition of the glass particles, a flow rate of the source material gas is 50% or lower with respect to a stable value (S1), the stable value (S1) that ranges from 90% or higher to 100% or less with respect to a maximum flow rate (M1) of the silica glass source material gas, a flow rate of the silica glass source material gas in a final deposition among the multiple times of deposition of the glass particles is the maximum flow rate (M1) of the silica glass source material gas, and a temperature of the etched surface of the core preform at a start of the deposition step is 50°C or higher. <EOS>