At the time of sterilization cleaning, the contaminants in the ultrapure water production system are not supplied to the supply pipe to the water use point, and after sterilization cleaning, the system is contaminated by contaminants captured by the particulate removal membrane. Prevent and supply ultra-pure water with good water quality to the water use point (use point) in a short time. In the ultrapure water production system including at least the tank 11, the pump 12, the heat exchanger 13, the ultraviolet ray device 14, the ion exchange device 15, and the first particulate removal membrane device 16, it is parallel to the first particulate removal membrane device 16. The second particulate removal membrane device 17 is provided to supply a part of the sterilizing water and the flushing water to the first particulate removal membrane device 16 and discharged from the water supply side to the concentrated water side without passing through the membrane, and the remainder Is passed through the second particulate removal membrane device 17. 殺菌洗浄時においては、水使用ポイントへの供給配管に超純水製造システム内の汚染物質を供給することなく、また、殺菌洗浄後においては、微粒子除去膜で捕捉された汚染物質によるシステム汚染を防止して、短時間で良好な水質の超純水を水使用ポイント（ユースポイント）に供給する。少なくともタンク１１、ポンプ１２、熱交換器１３、紫外線装置１４、イオン交換装置１５、第１の微粒子除去膜装置１６を備えた超純水製造システムにおいて、該第１の微粒子除去膜装置１６と並行に第２の微粒子除去膜装置１７を設け、殺菌水及びフラッシング水の一部を第１の微粒子除去膜装置１６に供給して、膜透過させずに給水側から濃縮水側へ排出し、残部を第２の微粒子除去膜装置１７に通水する。
