The invention relates to a filter device (10) for filtering a liquid, in particular a hydraulic oil, having a substantially cylindrical filter housing (12), which accommodates a filter element (30) and can be closed off by means of a cover (18), the filter element (30) having an associated untreated region (70) with an inlet (22) for supplying liquid which is to be filtered and a clean region (74) with an outlet (26) for removing filtered liquid, and the filter element (30) comprising an end plate (58) which is remote from the cover (18) and on which there is mounted a radially acting sealing element (62) for sealing the untreated region (70) of the filter element (30). To develop a filter device of this type in such a manner that it can be produced at lower cost and can be assembled more easily, according to the invention it is proposed that the sealing element (62) comprises a radially protruding sealing lip (64) which bears against the inner side of the filter housing (12) and is inclined toward the untreated region (70) of the filter element (30).