PURPOSE: To make it possible to replace only a filter medium by a method wherein the filter medium is placed on a lower packing material which is mounted on lateral frames of a lower frame, the both ends of the filter medium are fitted on the outer sides of longitudinal frames of the lower frame, and then an upper frame is fitted on the lower frame to install the filter medium.

CONSTITUTION: On the inside of an upper frame 1, a lateral frame 2a on which a corrugated upper packing materials 3 is mounted is provided, and at the same time, on the opposite side also, the upper packing material 3 is mounted to provide the upper packing materials 3 symmetrically, and longitudinal frames 2b which are connected to the lateral frames 2a at right angle are equipped. In the meantime, a filter medium 4 for a filter is formed into a corrugated shape for the purpose to increase the surface area. Also, on the inside of a lower frame 5, a lateral frame 6a on which a corrugated lower packing material 7 is mounted is provided, and on the opposite side also, the lower packing material 7 is mounted to provide the lower packing materials 7 symmetrically, and the lower frame 5 consists of the lateral frames 6a and longitudinal frames 6b which are connected to the lateral frame 6a at right angle. In the upper frame 1, the lower frame 5 is insertion-fitted, and at the same time, the filter medium 4 is held being pinched between the upper packing material 3 and lower packing material 7. In addition, on the outside of the longitudinal frames 6b of the lower frame 5, a spacer 8 made of a foam molded flexible resin is mounted.