Abstract: The rotating drum filter includes a filter cake cleaning-off unit operating with pressurized air for cleaning the filter cake off the outer jacket surface of a horizontally lying drum. The filter cake that has been removed shall not be given the chance to subsequently settle on the outer jacket surface due to an air-flow. To this end, the housing of the filter is partitioned vertically in an upper filter zone and a lower filter cake settling zone, with the exception of a cleaning-off zone located between these zones, which partition is made as air-tight as possible. The bottom of the upper filter zone includes discharge flaps via which filtered air deposited in the upper filter zone is removed. Accordingly, such dust can no more settle onto the jacket surface of the drum.