Abstract: Waste wood, such as stumps and snag, is treated to make it suitable for the production of paper pulp, whereby the raw waste wood is initially crushed so that part of the bark, sand and stones attached to the wood is detached at this stage already, the obtained crushed material is fed into a washer tank for further washing away bark, sand, stone and peat material from the wood, high-pressure water nozzles being provided at an inlet end of said washer to impinge strong water jets on the crushed wood material, and flow creating means being provided at the lower part of the washer tank to produce a water flow directed slantedly upwards towards an outlet end of the washer tank in order to entrain heavy wood fragments, which may tend to sink into the material leaving the washer tank at said outlet end thereof, said material being further after-crushed and sieved to separate an accept fraction thereof for feeding to a pulp production process.