In production of ultrapure water by purifying primary pure water with a secondary pure water manufacturing apparatus and a tertiary pure water manufacturing apparatus, high-purity ultrapure water is produced, wherein generation of hydrogen peroxide is minimized and the concentrations of TOC, DO, and hydrogen peroxide are reduced to the limit. In an ultrapure water manufacturing system, each of the secondary pure water manufacturing apparatus and the tertiary pure water manufacturing apparatus includes an ultraviolet oxidation device and a deionization device, downstream therefrom, by using an ion exchange resin. UV light control is performed in such a way that the hydrogen peroxide concentration results in 1 to 30 μg/L and the TOC concentration results in 1 to 10 μg/L at the outlet of the ultraviolet oxidation apparatus of the secondary pure water manufacturing apparatus and, in addition, the TOC concentration results in 0.1 to 5 μg/L at the outlet of the ultraviolet oxidation apparatus of the tertiary pure water manufacturing apparatus. UV light control is performed in such a way that the TOC concentration results in 1 to 10 μg/L at the outlet of the ultraviolet oxidation apparatus of the secondary pure water manufacturing apparatus and, in addition, the hydrogen peroxide concentration results in 1 to 20 μg/L and the TOC concentration results in 0.1 to 5 μg/L at the outlet of the ultraviolet oxidation apparatus of the tertiary pure water manufacturing apparatus.