PURPOSE: To achieve the miniaturization of an apparatus and the reduction in operation cost, by allowing a salt based on calcium and carbon dioxide generated from the high temp. place of a brine desalting apparatus due to a multi-stage evaporation method to dissolve in distilled water obtained from said desalting apparatus.

CONSTITUTION: Brine being raw water is supplied to a system from a pipe 6 and, after a scale preventing agent is at first added to the brine by an injection apparatus 3, the treated brine is successively flowed through the pipe of the condenser 5 of each evaporation chamber 2 from a low temp. stage to a high temp. stage and successively heated to a higher temp. by steam generated from the evaporation stage thereof. Subsequently, the heated brine is further heated by high temp. steam sent from, for example, a boiler through a pipe 7 in a brine heater 1 to be supplied to the high temp. evaporation stage of the evaporation chamber 2 and thereafter, flash evaporation is repeated to discharge the brine out of the system from the final low temp. evaporation stage through a pipe 8 while steam generated in each evaporation stage is condensed in the outside of the pipe of the condenser 5 to obtain distilled water.