PURPOSE: To enhance concn. efficiency by increasing the supply amount and holding amount of a liquid to be conc. in an evaporation surface, by bringing the side surface of trough for storing the liquid to be conc. in a supply part of said liquid to a downwardly directed, steeply inclined surface.

CONSTITUTION: In a concn. apparatus of seawater utilizing solar energy, thin plates Em, En each having an evaporation part, to which an absorbing layer Sm to be conc. is layed, are laminated to a vertical direction so as to provide an interval therebetween. Steeply inclined surfaces 2 are provided to the side edges of troughs Cm, Cn or storing seawater partially provided to the thin plates Em, En. By this structure, the water head difference between the surface of seawater in the trough Cn and the lowermost point of the steeply inclined surface 2 of the thin plate Em becomes short and a water head difference required in supplying seawater can be reduced. In addition, the interval between the thin plates Em, En can be made narrow and the heat transfer resistance of a space can be reduced.