An ultrapure water production apparatus includes: a receiving unit that accepts water to be treated; a first pump that feeds the water to be treated; an ultraviolet irradiation device at a secondary side of the first pump to perform ultraviolet oxidation treatment; an oxidizing substance removal device remove at least oxidizing substances from the outlet water of the ultraviolet irradiation device; and a second pump installed at a subsequent stage of the oxidizing substance removal device to feed outlet water of the oxidizing substance removal device as ultrapure water. At least a portion of the ultrapure water produced is circulated to receiving unit. The oxidizing substance removal device includes a chamber positioned between an anode and a cathode, and filled with an ion exchanger. At least a portion of the ion exchanger is an ion exchanger on which a metal catalyst is supported.

Provided is a pure water production device including an ultraviolet oxidation device for treating TOC components in water to be treated, in which an amount of water to be treated increases or decreases by 5 flow % or more with respect to a set value, and the pure water production device includes: a detection means for detecting an index directly or indirectly related to a concentration of H.sub.2O.sub.2 downstream or upstream of the ultraviolet oxidation device; and a control means for controlling an amount of ultraviolet rays in the ultraviolet oxidation device based on a detection value of the detection means.