To save a mechanical cost for separation with density and also to make clear result of the separation by pulverizing trash mixture particles to smaller solid particles than a specific size, making wet and dry, mixing with separation fluid, separating, and then classifying the solids into portions having different density.

The trash mixture containing contaminated plastic scrap chips reduced the size to ≤ about 15 mm with a pulverizer, is immersed into liquid, etc., at a wet silo 11. Later the contaminated plastic scrap chips are crushed with a friction drier 13 and also is separated one portion 25 of the immersing water. Thus, the plastic scrap chips are isolated from the impurities. Consequently these are mixed with the separation liquid at a mixing tank 15, then the impurities are separated from the plastic scrap chips with a sorting centrifugal separator 19, and also the separation liquid is separated from solid particles. The plastic scrap chips are discharged as a lighter portion 21 and separated foreign particles are discharged as a heavier portion 20.