PROBLEM TO BE SOLVED: To provide an operation method of an apparatus for producing medical purified water, which can be sterilized by using hot water.SOLUTION: The apparatus for producing medical purified water is sterilized by steps of: heating RO water in a RO water tank 6 by using a heater 6a to rise a temperature of the RO water； and circulating the heated RO water in a circulation line including an activated carbon device 2, a NF device 3 and a RO device 5. After the apparatus is sterilized, the apparatus is cooled by the steps of: cooling the RO water in the RO water tank 6 by using a heat exchanger 8 to lower the temperature of the RO water； and circulating the cooled RO water in the circulation line.【課題】熱水殺菌できる医療用精製水の製造装置の運転方法の提供。【解決手段】ＲＯ水タンク６内のＲＯ水をヒータ６ａで加熱昇温させながら、活性炭装置２、ＮＦ装置３、ＲＯ装置５を含む循環ラインに循環させて殺菌する。殺菌後、ＲＯ水タンク６内のＲＯ水を熱交換器８で冷却降温させながら、前記循環ラインに循環させて冷却する。【選択図】図１
