To provide an apparatus and a method by which moisture can be efficiently evaporated from matter to be dried and the grain size of a recovered solid can be optionally changed.

As a heat source for recovering the solid by evaporating the moisture from the matter to be dried, heat generated from a burner is sent to the inside of a cylindrical plate to directly heat the cylindrical plate. The matter to be dried which is finely pulverized by a spray nozzle or an ultrasonic sprayer is sprayed onto an outer surface of the heated cylindrical plate to instantly evaporate the moisture and deposited solid is scraped off by a scraper. Waste heat passed through the inside of the cylindrical plate is used as a heat source of a concentrator for pretreatment of the matter to be dried and to preheat the matter to be dried. Further heat exhausted from an outer surface of a hot air furnace for burning with the burner is used to concentrate and preheat the matter to be dried. The solid-liquid separator of this invention has constitution described above.