To realize efficient evaporation-condensation with an apparatus smaller in size and inexpensive in production cost, by installing a heat exchanger on a condensation part in such a way that on one side surface of a thin plate bending continuously and reciprocally circulation gas flows and that the open air flows on the other surface of the thin plate.

A condensation part (a heat exchanging part) 21 installed on an upper frame 20 is mainly composed of an axial fan F and a heat exchanger 210. The heat exchanger 210 processes the first channel which connects a channel L1 to a channel L2 for gas circulation and the second channel which connects the inlet to the outlet for the open air sent by the axial fan F, and both channels of the heat exchanger 210 are so structured that four surfaces around a continuously bent thin plate are closed by walls on four sides. Both ends of the bent thin steel plate are unified by being sealed with an adhesive to the fixed walls on the light and left sides to prevent gas leakage. The condensate obtained by heat exchange in the heat exchanger 210 is discharged to a condensate tank 80 through a drain D.