A filter element has a wavy filter portion including a plurality of ridges of a filter material, which are juxtaposed to one another and closed at their sides, and a flange portion extending along a mounting plane around the filter portion for supporting the filter portion. The flange portion is made of the same filter material extending from the filter portion, by compressing the filter material more densely than the filter portion. The filter element is manufactured by a step of preparing an intermediate product of a wavy sheet, and a step of forming the filter portion by leaving the central portion of the wavy intermediate product as in the wavy sheet, and forming the flange portion around the filter portion for supporting the filter portion, by pressing the side portions of the ridges of the wavy intermediate product along the mounting plane.