PURPOSE: To break consolidation due to sludge mechanically and to recover a filtering function by a mechanism wherein working faces are arranged on a bed surface portion of a sludge drying filter bed and deposited sludge and the bed surface portion are agitated all over the surface.

CONSTITUTION: Working faces 7 to which a large number of rolling pawls 8 as the rotors of an agricultural cultivator are installed are disposed to a consolidated sludge layer 4 on a filter layer of a filer bed, such as a sun drying filter bed, etc. The rolling pawls 8 are rotated at slow speed at a location where the pawls reach the consolidated sludge layer 4. Thus, sludge with high density and low density is mixed, the flow paths of filtered water are formed in the consolidated sludge layer 4, and the filtering effect of the filter bed is recovered.