Abstract: A machine for cleaning walls such as the reactor cavity walls in a nuclear power plant by means of at least one rotatable roller brush. For cleaning machines that must be used hanging by wires it is difficult to achieve a sufficient bearing pressure against the wall to be cleaned. Especially in deep cavities the bearing pressure decreases the longer the cleaning machine reaches into the cavity. The problem has been solved by using a roller brush comprising a plurality of soft grinding sheaves which are axially compressible and decompressible for changing the density of the roller brush and by having counterweight means provided with means for increasing or decreasing its weight and thus changing the weight distribution of the machine for changing the bearing pressure of the machine against the wall.