PURPOSE: To save power and energy and to evade the rupture of an effective component such as vitamins by drying a slurry such as condensed milk supplied on a conveyor utilizing a heater by a solar water heater.

CONSTITUTION: Hot water is sent from a solar water heater 6 to a hot-water heater 5 provided on the lower surface of a belt conveyor 1 at its region 4 on which a slurry is traveled, and condensed milk 9 is thinly spread over the operated conveyor 1 from a feeder 2. The liq. in the milk 9 traveled by the conveyor 1 at about 1m/sec is vaporized by the heater 5, and only the powdery solid is left after the heater 5, scraped off by a scraper 11, dropped into a product receiver 3 and accumulated. Consequently, the power cost is reduced as compared with the conventional process utilizing an electric heater, and the effective material such as vitamins is never ruptured by the high temp.