NOVELTY - The system (1) has a preprocessor (20) that adds a ferrous salt coagulant to salt water for filtering impurity in salt water so that pH value of the salt water is reduced. An electrodialyzer (30) is provided for adding chemical substance in salt water so that the salt water is separated into dilution water with low salt concentration, and concentrated water with high salt concentration. A reverse osmosis membrane type desalinator (40) is provided for separating the separated concentrated water and separated dilution water into fresh water.    USE - Desalination system for removing salt content from seawater.    ADVANTAGE - The electrodialyzer is provided for adding chemical substance in salt water so that salt water is separated into dilution water with low salt concentration, and concentrated water with high salt concentration. Hence the procurement of chemical substance in desalination system is reduced. The requirement for transporting and storing the chemical substance is reduced.    DETAILED DESCRIPTION - A mixing line structure is provided for mixing salt water before the impurity of salt water is removed by the preprocessor. The caustic soda supplied from a caustic soda line structure is mixed with chlorine generated in the anode of the electrodialyzer for generating sodium hypochlorite in the electrodialyzer where the cathode of the electrodialyzer is the caustic soda. A freshwater line structure (L4) is provided for supplying freshwater flown out of the reverse osmosis membrane, as a catholyte to the electrodialyzer. An electric power generating apparatus is provided for utilizing hydrogen generated in the cathode of the electrodialyzer so that the required electric power is generated in a desalination structure.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of desalination system.(Drawing includes non-English language text)    Desalination system (1)    Preprocessor (20)    Electrodialyzer (30)    Reverse osmosis membrane type desalinator (40)    Freshwater line structure (L4)