Problem to be solved: To facilitate setting on a container. Solution: Leg piece parts 5, 5 are provided on the right and left of an opening 4 opened in a substrate 2, and connection piece parts 6, 6 are provided on the front and rear sides. A first folding line part 9 is formed in the center of the leg piece parts, and a second folding line part 10 is formed in both end parts 6 a, 6 a of the connection piece parts. A filter bag 3 is fixed to the lower surface; Both ends of the connecting piece are folded to the lower surface side with respect to the folding line part 10, thereby folding the leg piece in a flat shape, and at the same time, aligning them in parallel to hold the filter bag 3 between both leg piece parts, and closing the opening 4 with the upper surface sides of the front and rear connecting piece parts closer to each other, and closing the filter bag 3 to form the filter 1. The filter is used to open the opening (4) by opening the connecting piece (6) back and forth, and make the left and right leg ends (5) stand up and set in a settable state. Selected drawing: Figure 5
