PURPOSE: To improve heat exchange efficiency and to rapidly prepare distilled water, by directly heating a small heating chamber by a burner while heating the same in a conc. state by radiant heat through a reflective mirror.
CONSTITUTION: Radiant heat from the flame 5 of a burner 4 is directly transmitted to a heat exchange unit 40 and also transmitted thereto through a reflective mirror 3a. A small amount of water in the heating chamber 14 is heated in a conc. state while steam is cooled by a cooling chamber 16 to be converted to distilled water. When the water in the heating chamber 14 is reduced, a float is moved downwardly and water in a preheating chamber 11 is flowed into the heating chamber 14 through the valve 9 for feeding water to said heating chamber 14.