The inventive device for filtering contaminated liquids, e.g. coolant lubricants in workpiece machining, comprises a liquid container (11) with an inlet (13) for the contaminated liquid and an outlet (15) for the filtered liquid. A filtration element which can be connected to the outlet is located in the liquid container. The invention aims to guarantee the high liquid throughputs through the filtration element which are required, in particular, during a full-flow filtration, whilst maintaining the smallest possible surface area and volume requirement for the container. To this end, the filtration element (18) essentially consists of a filter drum (19) which can be mounted in the liquid container (11) in a fixed manner in relation to the latter, with a filter element (25) which is provided on its periphery. Said filter element can be cleaned by a mobile cleaning device (28) which can be displaced along the peripheral surface of the drum. As the filter drum is fixed in the liquid container, it can be connected directly to the feed pump for the purified filtrate via a suction pipe, without the need for expensive rotary feedthrough. The feed pump evacuates the filtrate directly from the filter drum, thus generating a relatively high negative pressure inside the latter. Said negative pressure significantly increases the liquid throughput through the filter element, in comparison with conventional full-flow filtrations of the same surface area.