PURPOSE: To prepare a high-quality fiber for paper making from a raw material obtained by coarsely breaking waste paper containing small pieces of plastic film, aluminum foil, etc., while saving energy.

CONSTITUTION: A raw material obtained by coarsely breaking waste paper is supplied to the first separator 31 equipped with a perforated plate having many holes of a suitable diameter corresponding to the degree of fine selection and with a screen having slits of a suitable size and the fibers allowed to pass through the screen are recovered. The material not allowed to pass through the holes of the perforated plate is supplied to the second separator 32 equipped with a perforated plate having many holes of a suitable diameter and the material not allowed to pass through the holes is discharged. The paper stock allowed to pass through the holes of the second separator and the material not allowed to pass through the screen of the first separator are supplied to the third separator 33 equipped with a screen having slits of a size almost same as that of the first separator. The material not allowed to pass through the slits is discharged and the fibers allowed to pass through the slits are recovered and supplied together with the fibers recovered by the first separator to next process.