To improve the efficiency for removing impurities in no sorting treatment of a waste paper.

The impurities are removed by inserting not only newspaper and leaflets but also a waste paper of a magazine, a book or the like having subsidiaries made of resin sheets such as filed bag for a CD mixed therewith without sorting them to a main breaker 1 to form a fiber suspension, subjecting the fiber suspension to auxiliary disintegration by an assistant breaker 2 to disintegrate unbroken components, discharging the broken product through a discharging screen comprising a hole screen having ≥2.2mm eyelets, and passing the screened product through a hole screen having ≥1.4mm eyelets and a slit screen having ≤0.15mm slit width. The resin impurities having various sizes can be efficiently removed by combining the sizes and kinds of the screens.