PURPOSE: To carry out solvent removing treatment with no need of complex operations by adding a liquid which is supplied by a liquid supplying means to a dissolving solution which is sent by a liquid sending means and mixing the liquids each other.

CONSTITUTION: A powder granule mixing apparatus 1a comprises a precipitant supplying means 2 to supply a precipitant, a solvent supplying means 3, a mixing and dissolving part 4, a liquid sending means 5, and a liquid supplying means 7. The mixing and dissolving part 4 has a column 20 and a circulating means 6 is installed in the column 20. Mixing and dissolution of a precipitant Pr is accelerated by circulating a liquid in the column 20 by the circulating means 6. The end part in upper stream side of a pipeline 30 and the end part in the down stream side of the pipeline 30 are respectively connected with the near bottom part of the column 20 and a pipeline 18 through a T-shape branched connector 33 and a dissolving liquid S1 and blood plasma Po join and are mixed each other in the branched connector 33 and high molecular weight protein substances in the blood plasma Po precipitate. In this way, powder granules are prevented from flowing out.