PURPOSE: To attain the desalting of sea water as well as make it possible to use the air after heat exchanged in cooling and warming an interior of a room by utilizing the solar energy and the natural convection of air as a heat collecting medium.

CONSTITUTION: The sea water is supplied to a lower inlet of a heat exchanger from a copper tube a. The heat collected air is heat exchanged with the sea water within a heat exchanger and the heated sea water is introduced to an evaporating dish f and, herein, the evaporation is carried out to obtain fresh water. At the same time, the air after heat exchanged is discharged into a room and utilized in cooling or warming said room.