To provide a system, a method and a material which do not require an exact processing control method and an internal filter capable of using an economical material.

In an internal filter having a comb fluid passage connected with a plurality of filter holes 130 and interleaved, a fluid arrives at an extension part 122 of an outlet side passage 120 from an extension part 112 of an inlet side passage 110 through the filter holes 130. The fluid in the inlet side passage 110 contains particles having dimensions and shapes which are not able to pass through the filter holes 130 and a considerable number of particles are eliminated from the fluid arrived at the outlet side passage 120 compared with the fluid at the inlet side passage 110 by the filter holes 130.