The purpose of the present invention is to provide technology for regenerating pulp having high quality with compact pulp regenerating equipment and less energy. In the pulp regenerating method of the present invention, pulp slurry containing 1.5 wt% or more of a solid component including waste paper pulp is separated into a long fiber fraction and a short fiber fraction by using an outward type slit screen including an opening portion having a slit width in the range of 0.1 mm to 0.3 mm. The solid component ratio of the long fiber fraction and the short fiber fraction is in the range from 10:90 to 60:40, and the difference in Canadian Standard Freeness of the long fiber fraction and the short fiber fraction is in the range of 100 ml to 300 ml.