To provide a pure water producing facility capable of producing pure water with high purity without replacing ion-exchange resin for a long time, and to provide a method of elongating the service life of the ion-exchange resin.

The pure water producing facility includes: a filtering device 10 removing impurities included in raw water; an RO membrane device 20 reducing dissolved ion components included in filtrate water passed through the filtering device 10 to 20 mg/L or less in total; and an ion exchange device 30 making treatment water passed through the RO membrane device 20 sequentially come into contact with cation-exchange resin and anion-exchange resin to produce pure water.