A filter element made of nonwoven filter fabric includes a plurality of pleated portions and a flange portion formed integrally with the filter portion. The flange portion is formed by a pair of press-forming dies to have a thin and compressed connecting portion formed along the outer periphery of the filter portion, a thick and uncompressed seal portion formed along the outer periphery of the connecting portion and a thin and compressed protecting portion formed along the outer periphery of the seal portion.
