A filter device comprising a filter (2) for filtering liquid filling a first container (1), a second container (3) for storing the liquid filtered through the filter (2), a third container (7), a first line (4) connecting the first container (1) and the filter (2), a second line (5) connecting the filter (2) and the second container (3), and a third line (6) branched off from the second line (5) and connected with the third container (7). The third container (7) is disposed above the second container (3) with a section connected with the third line (6) directed downward. The second container (3) is disposed below the first container (1) and formed such that it can be deformed by an external force and restored when the external force is removed.