A filter element for filtering slurry liquid, the filter element comprises a layered member of nets and non-woven fabrics in which each of the nets and the non-woven fabrics are alternately layered,
- wherein each of the nets has first fibers parallelly extending in one direction and second fibers parallelly extending in a direction angled to the one direction and contacting sides of the first fibers, wherein the first fibers and the second fibers forms mesh-pores at portions surrounded by the first fibers and the second fibers in each of the nets,
- wherein each of the nets has one surface in which the first fibers are parallelly provided with a predetermined distance and another surface in which the second fibers are parallelly provided with a predetermined distance, the one surface is an opposite surface of the another surface,
- wherein pits are formed between each of the first fibers on the one surface of the each of the nets and between each of the second fibers on the another surface of the each of the nets, thickest protrusions of the nets being formed at crossings of the first fibers and the second fibers of the nets, and mesh-pores are formed in portions surrounded by the first fibers and the second fibers,
- wherein fiber diameters of the each of the first fibers and the second fibers of the nets range from 250 micrometers to 350 micrometers in average, and the predetermined distances of the first fibers and the second fibers of the nets is 900 micrometers in average,
- wherein each of the non-woven fabrics has protrusions on surfaces of each of the non-woven fabrics in a thickness-direction that is a direction along a thickness of each of the non-woven fabrics, the protrusions of the non-woven fabrics being defined as portions that are higher than an average surface height around the protrusions of the non-woven fabrics and the protrusions do not reach ¼ of a thicknesses of the net at each of the mesh-pores, and
- the protrusions of the non-woven fabrics are repeatedly formed on the surfaces of each of the non-woven fabrics in a direction within a plane of each of the non-woven fabrics,
- wherein the fibers in the non-woven fabrics comprise 80 percent of the fibers having fiber diameters within a range of 20 micrometers to 30 micrometers, and 20 percent of the fibers have fiber diameters that exceed 50 micrometers,
- wherein a size of the protrusions of the non-woven fabrics have widths of 1000 micrometers, lengths of 4000 micrometers, and 800 micrometer peak heights in average values,
- wherein each of the protrusions of the non-woven fabrics are positioned at a portion where each of the protrusions of the non-woven fabrics contact one of the crossings of the first fibers and the second fibers of the nets, or meets each of the mesh-pores of each of the nets, a portion where each of the protrusions of the non-woven fabrics contact one of the crossings of the first fibers and the second fibers of the nets is a portion where each of the protrusions are a thickest portion in the net and each of the protrusions have a peak-thickness portion in the non-woven fabric that intersect with each other, and
- at least one of the protrusions of the non-woven fabrics does not come into at least one of the mesh-pores of the nets at the portion where each of the protrusions of the non-woven fabric meet each of the mesh-pores of each of the nets.