PURPOSE: To perform concn. of good efficiency with relatively simple construction by locating the lower part of the open terminal of a lead-in piping for raw material solns. approximately at the center in a vacuum evaporation chamber of an inverted circular cone shape, and directing the same downward.

CONSTITUTION: The raw material dope which has been preheated prior to entering a charging pump 1 and has further been preheated in a heater 2 to a prescribed temp. is flushed from the open terminal 3 of the lead-in piping onto a vacuum evaporation chamber 4. While the flushed dope is being lost of part of solvents by evaporation, it arrives at the vessel wall. While flowing down the wall surface, it is further evaporated of solvents and gathers in the vessel bottom as the concd. dope, from which it is discharged and recovered by a pump 6 through a discharge piping 5. The evaporated solvents are conducted by a vacuum pump 7 to a piping 8, and are liquefied by a condenser. The liquefied solvents are recovered and stored in a tank 10. Therefore, the solvents are recovered advantageously from high viscous liquid with the relatively simple construction.