To make treated water reusable and lower the load of the wastewater treatment thereafter by using a chelating polymer flocculant of maceration and steam maceration wastewater in paper manufacturing process and adjusting the wastewater neutral or acidic.

After waste paper 6 is macerated by a macerator 1, a chelating polymer flocculant 2 is added to control pH at neutral or lower. In this case, the addition amount is preferably controlled to adjust the pH around 6. After that, the resultant macerated waste paper is washed in a concentrated wastewater washing apparatus (a thickener) 3 and divided to a paper manufacturing substance 4 and washing wastewater 5. By such treatment, COD and BD in the wastewater are significantly lowered and pH adjustment is made unnecessary and the SS and the COD values in the separated water is remarkably decreased and flocculation and precipitation treatment is easily carried out, so that repeat use of the treated water is made possible. Further, dewatering efficiency of cellulose is greatly increased and recovery efficiency is heightened. Furthermore, PVA is made reusable. As the chelating polymer flocculant 2, a mixture of a chlorine type inorganic flocculant and a polyamine type flocculant is especially preferable.