This desalinization system, which obtains industrial-use water and drinking water from seawater and wastewater, is provided with: a purification device that purifies wastewater by removing activated sludge therefrom; a first RO membrane that removes salt from the output of the purification device by transferring said salt to first concentrated water, thereby producing industrial-use water; a UF membrane that seawater passes through and that removes particulates from said seawater; a second RO membrane that removes salt from the treated output of the UF membrane by transferring said salt to second concentrated water, producing drinking water; an agitation device to which the second concentrated water from the second RO membrane and the first concentrated water from the first RO membrane are sent to be agitated; and a third RO membrane removing salt from the liquid mixture agitated by the agitation device by transferring said salt to third concentrated water, producing industrial-use water.