PURPOSE: To obtain the best pure distilled water free of impurities such as air and CO2 by heating pure water in a heating kettle to degas the pure water, evaporating the pure water in an evaporator, cooling and condensing the vapor in a condenser.

CONSTITUTION: Pure water 3 is introduced into a heating kettle 1 to a level L1 and heated to 120°C, for example, by an electric heater 2, and the air, CO2, etc., in the pure water 3 are discharged into a vapor chamber 4. The pure water 3 with the purity improved is allowed to flow down into the central tube 20 of an evaporator 19 through a passage 18, and pure water is heated by the high-temp. vapor supplied to an outer tube 22 from the vapor chamber 4 through a passage 21 and evaporated. The vapor is introduced into condensers 41 and 44 from an evaporation chamber 37 through a passage 39, cooled by cooling water supplied from an inlet 49 and condensed to obtain pure evaporated water. The pure evaporated water is transiently stored in a tank 47, discharged through a water valve 69 and used in manufacturing medicine, etc.