To permit easy and clean operation of replacing a filter and easy recovery of a liquid within a housing, and improve filter replacing workability.

A filter unit 20 consisting of the filter 22 contained in a bag 21 is housed within the housing 10 with the bottom part 21a of the bag 21 folded so that a liquid in the bag 21 is prevented from flowing in the bottom part 21a, and the filter 22 can be exchanged as the unit 20. When the unit 20 is removed from the housing 11, the tendency that the liquid in the bag 11 tends to flow into the bottom part 21a and makes the bag 11 press toward the inside wall of the housing 11 is eliminated, thus facilitating the removal of the unit 20.