PURPOSE: To increase purifying treating power, dusting ability and disaggregating ability by providing a closed casing with a screen and impeller in a specific state and dividing a fiber recovery chamber into a fine selecting chamber and a coarsely selecting chamber.

CONSTITUTION: A closed casing 3 provided with a raw material feed opening 1 and a foreign matter outlet 2 is equipped with a screen 4 and divided into a fiber recovery chamber 6 and a foreign matter recovery chamber 5. An impeller 7 is rotatably set at the side of the foreign matter recovery chamber close to the screen 4, part at the outer peripheral side of the screen is made into a finely selecting part 41 and part at the inner peripheral side into a coarsely selecting part 42, which are made to correspond to a finely selecting chamber 61 and a coarsely selecting chamber 62 divided by a partition plate 10 and the chambers are provided with outlets 8 and 9, respectively.