A degassing device (10), a hydrogen dissolving device (12), and a palladium catalyst column (17) are provided in that order downstream of a high-purity water production device (1), and an impurity removal device (19) is connected to the exit side of treated water of the palladium catalyst column (17). The impurity removal device (19) removes impurity ions which are eluted into the water to be treated or impurity particulates which mix in with the water to be treated during the treatment in the palladium catalyst column (17). The impurity removal device (19) comprises an ion exchange device (20) and a membrane treatment device (21) such as a ultrafiltration membrane device, a reverse osmosis membrane device or the like. By providing an impurity removal device (19) in this manner, it is possible to remove impurities generated during hydrogen peroxide removal treatment by the palladium catalyst and to prevent degradation in quality of hydrogen-dissolved water.