PURPOSE: To simplify the piping by a method wherein when a first filter functions, a backing pressure is generated at a second flowing-out port side of a second filter, and when the second filter functions, a backing pressure is generated at a first flowing-out port side of the first filter.

CONSTITUTION: A first flowing-out port 36a communicates with the inside of a second filter chamber 30b by a passage 38, second flowing-out port 37a, and a small hole 35c on a filter shaft 35b of a partitioning plate 3 which divides a second filter chamber 30b. Then, a backing pressure is generated on a second filter 50 side by a solvent which flows out from a first filter 40 side. For this reason, when the first filter 40 functions, foreign object which is adhered to the second filter 50 is diffused by the backing pressure. Also, when the second filter 50 functions, a backing pressure is applied to the first filter 40 side, and foreign object which is adhered on the first filter 40 is diffused. As the result, even when a filter device F is used for a long period of time, a clogged condition due to foreign object, etc., can be suppressed.