An apparatus for producing a polymer, wherein the surface of a member contacting with the polymer of a device for melting and molding a raw material polymer has been subjected to a passivation treatment and is covered by a passive film, wherein ultra-pure water is used as a solvent to be injected into a molten polymer, to prevent the incorporation of a contaminant, and wherein an inert gas is fed to the line for discharging a gas, to prevent the contamination by back diffusion. As the above passive film, an aluminum oxide film or a chromium oxide film is preferred.