The invention relates to a method and device for the washing of a medium consistency fibrous slurry, especially a chemical pulp slurry in which the slurry is fed at an inclined angle onto a substantially horizontal portion of circulating filter belt, and then distributed over substantially the entire working width of the filter belt. The distributed slurry is then washed with a washing liquid under localized pressure to produce a slurry having a medium consistency range, i.e., about 8 to 15 percent. In order to increase the consistency to 20 to 40 weight percent, preferably about 30 to about 35 weight percent, the washed slurry is passed to a pressing zone.