PURPOSE: To improve the performance of an evaporating condenser remarkably by a method wherein the fluid of high-temperature cycle side is flowed down and evaporated at the outer surface of both surfaces fluted tubes by providing a liquid distributing plate while the gas of low-temperature cycle side is condensed on the inner surface of the same tubes.

CONSTITUTION: In the evaporating condenser of the cascade cycle type heat converting system, a medium A to be condensed or steam flows into an upper prenum chamber 8 and is condensed while flowing through the inside of a multitude of both surfaces fluted tubes 11. Condensed liquid, flowed down along the wall surfaces of the tubes is reserved at the bottom of a lower prenum chamber 9 and is discharged to the outside of the system. On the other hand, the medium B to be evaporated or a liquid is supplied on the liquid distributing plate 12 in a shell 6 and is evaporated (flow down liquid film evaporation) while flowing down along the outer surfaces of the both surfaces fluted tubes 11. The liquid, not evaporated yet, is reserved at the lower part of a heat exchanging chamber 10 and pool evaporation is caused here. The vapor flows through the inside of a heat exchanging tube 13 via a connecting pipe 14 and is heated here by the condensed medium A and is discharged to the outside after liquid drops, mixed in the vapor, are evaporated.