A filtering device has a filter element disposed between the inlet and the outlet of the device. The inlet surface of the filter element is prone to clogging by suspended particles, e.g. waste, carried with the incoming raw fluid. The invention provides a cleaning head for the filtering device, comprising a basis and a nozzle movably mounted thereon. The cleaning head basis is mounted on a driving mechanism so that the nozzle can scan the inlet surface parallel thereto, and can clean the inlet surface by means of a backwash flow passing through the filter element into the nozzle under a cleaning pressure differential created by connecting the nozzle to a low-pressure outlet. The nozzle maintains, during scanning, permanent contact with the inlet surface so that lateral flow directly into the nozzle is essentially prevented despite variations of distance between the cleaning head basis and the inlet surface during the scanning.