A pillar-shaped honeycomb structured body comprises large-capacity through holes and small-capacity through holes, a first partition wall between two adjacent large-capacity through holes, a second partition wall between a large-capacity through holes and a small-capacity through holes adjacent to each other. Each of the plurality of large-capacity through holes and small-capacity through holes extends from a first end face to a second end face. An aperture rate α (%) is a ratio between the sum of the area of the large-capacity through holes at the second end face and the area of the second end face. The difference in the thickness of the first partition wall and the second partition wall is β (mm). The relationship between α and β satisfies the following inequalities (1) and (2): 0.0022α+0.0329≦β≦0.0071α+0.2553 (1), and about 35≦α≦about 60(2).