PURPOSE: To prolong the life of a filter material, to make the physical outside size thereof remain unchanged and to remove the transport loss by applying an ultrasonic wave to a material to be cleansed at the same time as the material is passed through a basin that contains a washing liq.

CONSTITUTION: The material 1 to be cleansed, for example, the filter material such as activated carbon and zeolite, is supplied with an injector 2 to the basin 3 which contains the washing liq. 4, preferably, an emulsion of water and oil. At this time, the material 1 to be cleansed is passed as a mat on a conveyor 5 while the ultrasonic wave from an ultrasonic wave generator 6 is being applied thereto. Then, impurities are separated from the material to be cleansed into the washing liq. 4 due to cavitation by the ultrasonic wave and the cleansed material 1 is transported outside the basin 3 by means of the conveyor 5, for example, a wire conveyor. The cleansed material 1 leaves the basin 3 and is then dried with a vacuum dryer 7, and is furthermore dried with a flushing 8 and an infrared dryer 9.