In controlling a sterile water production device, if pH of sterile water is smaller than a preset pH, an additional aqueous hypochlorite solution is injected into the sterile water to increase the pH back to the preset pH, and a molar quantity of residual alkaline impurities present in such additional aqueous hypochlorite solution is determined. Next, a predetermined amount of further additional aqueous hypochlorite solution is injected into the sterile water, wherein such predetermined amount is an amount required to yield additional content of hypochlorous acid in a resulting sterile water, to such a degree that a molar quantity of that hypochlorous acid is equal to the foregoing determined molar quantity of residual alkaline impurities. After such injection, pH of sterile water yielded is increased, and an acid aqueous solution is then injected into the sterile water to thereby decrease the increased pH back to the preset pH.