a porous body having a plurality of through holes extending in parallel with one another in a length direction of the porous body and a wall portion interposed between said through holes, said plurality of through holes includes ones sealed at one end and ones sealed at the other end,

wherein said plurality of through holes includes a plurality of large-capacity through holes opened on a flow-in side of said porous body and a plurality of small-capacity through holes opened on a flow-out side of said porous body, each of the large-capacity through holes has a relatively large area in a cross-section perpendicular to the length direction, each of the small-capacity through holes has a relatively small area in the cross-section, said large-capacity through holes and said small-capacity through holes have a substantially same number of through holes, said porous body satisfies relations, Y≤−1.1X+68.5, Y≤19, and 35≤X≤56, where Y represents a volume of said porous body in L and X represents an aperture ratio on the flow-in side in %.