PURPOSE: To provide a fresh water and cold sea water preparation device utilizing fresh water for drinking water or the like and also utilizing cold sea water for breeding fish, culturing Konbu (sea tangle) and the like by utilizing cold heat generatd at the time when LGN liquid is gasified to prepare LNG gas.

CONSTITUTION: LNG liquid running from an LNG supply pipe 16 through heat absorption instruments 18 and 19 absorbs gasified heat out of sea water in first and second tanks 1 and 2 to cool the sea water turned into gas, made to flow into an LNG supply pipe 21 and fed to the outside. The sea water cooled in the first tank 1 and made to flow into the second tank 2 is agitated and further cooled, and the salt content is separated outside at the time of freezing, and cleaned with fresh water, pumped up from a third tank 3 and jetted out of a nozzle 27 to be formed into ice not containing the salt content and floated up. The ice composed of pure water is passed through an overflow passage 7, dropped into the third tank 3 and turned into cold fresh water. The sea water to be introduced into the first tank 1 by a heat exchanger 10 is cooled by the sea water in the second tank 2 increased in the salt concentration due to the separation of ice and discharged as the cold sea water.