PURPOSE: To easily and efficiently concentrate a soln. in a method for concentration in the case of making salt from the sea water, etc., by supporting absorbers on an endless track, conveying the same and repeating the substitution of the soln. by utilizing the spraying and absorbing of the soln. as well as the evaporating and spraying of moisture.

CONSTITUTION: A driving device 6 of an endless trolley chain 5 is rotationally driven to turn the respective absorbers 2 hung to the chain 5 in an arrow direction. The sea water in a storage tank is sprayed to the absorbers 2 in a spraying chamber 8 so that the absorbers are sufficiently absorbed with the sea water. The evaporation stage to move the absorbers in the atm. is then started. The moisture in the sea water absorbed to the absorbers 2 is evaporated by the solar heat and the difference of the steam pressure from the atm., by which the sea water is concentrated. The sea water in the absorbers 2 and the sea water of the low concn. in the storage tank are substd. when the absorbers are further turned and conveyed to the spraying chamber 8 again. The sea water is gradually concentrated by repeating the above-mentioned operations.