PURPOSE: To obtain a solution containing a macromolecular solute at an accurately controlled concentration by filtrating and condensing the solution through a semipermeable membrane.

CONSTITUTION: Two facing covers 2 are stuck to an enclosure 1 and a pair of condensing units in arranged in the enclosure 1. Each condensing unit is provided with a chamber 9, an absorbent layer 7, and an elastic layer 8 and one wall surface of the chamber 9 is constituted of the rear surface of one cover 2. The other wall surface is constituted of a semipermeable film 6 having permeability to the solvent of a sample solution, but no permeability to a macromolecular solute, and the horizontal wall of the chamber 9 constitutes a projecting section 4. A frame 10 which is in close contact with the film 6 forms areas 10A, 10B, 10C, and 10D having permeability to the sample solution and the absorbent layer 7 keeps the solvent passed through the film 6. The elastic layer 8 presses the layer 7 against the film 6. Both units are separated from each other by a wall 11 and simultaneously but separately condense the sample solution. The sample solution is introduced from ports 3A and 3B and the condensed solution can be taken out with a pipette.