A honeycomb fired body comprising: a plurality of cells in each of which one end is plugged and which serve as channels of exhaust gas; and porous cell partition walls defining the cells wherein the honeycomb fired body is formed of SiC, the plurality of cells include peripheral cells (21, 21a, 21b, 21c, 21d, 21e) located at an outermost peripheral region of the honeycomb fired body and inner cells located more inward than the peripheral cells (21, 21a, 21b, 21c, 21d, 21e), all the inner cells have the same cross-sectional shape that is a rectangle in a plane perpendicular to the longitudinal direction thereof, each peripheral cell (21, 21a, 21b, 21c, 21d, 21e) is defined by the cell partition walls and an outer wall forming a periphery of the honeycomb fired body, the cell partition walls in contact with the outer wall each have a thick wall region where the wall thickness gradually increases toward the outer wall, the cross-sectional shape of the peripheral cells (21, 21a, 21b, 21c, 21d, 21e) in a plane perpendicular to the longitudinal direction thereof is a shape formed by reducing the rectangular cross-sectional shape of the inner cells to obtain a reduced rectangle and chamfering or rounding two corners of the reduced rectangle, the cell partition walls include inter-peripheral-cell cell partition walls each located between the peripheral cells (21, 21a, 21b, 21c, 21d, 21e) and inter-inner-cell cell partition walls each located between the inner cells, and the minimum thickness of the inter-peripheral-cell cell partition walls is greater than the thickness of the inter-inner-cell cell partition walls, characterised in that the cross-sectional area of each peripheral cell (21, 21a, 21b, 21c, 21d, 21e) in a plane perpendicular to the longitudinal direction thereof is 60 to 80% of the cross-sectional area of each inner cell in a plane perpendicular to the longitudinal direction thereof. a plurality of cells in each of which one end is plugged and which serve as channels of exhaust gas; and porous cell partition walls defining the cells wherein the honeycomb fired body is formed of SiC, the plurality of cells include peripheral cells (21, 21a, 21b, 21c, 21d, 21e) located at an outermost peripheral region of the honeycomb fired body and inner cells located more inward than the peripheral cells (21, 21a, 21b, 21c, 21d, 21e), all the inner cells have the same cross-sectional shape that is a rectangle in a plane perpendicular to the longitudinal direction thereof, each peripheral cell (21, 21a, 21b, 21c, 21d, 21e) is defined by the cell partition walls and an outer wall forming a periphery of the honeycomb fired body, the cell partition walls in contact with the outer wall each have a thick wall region where the wall thickness gradually increases toward the outer wall, the cross-sectional shape of the peripheral cells (21, 21a, 21b, 21c, 21d, 21e) in a plane perpendicular to the longitudinal direction thereof is a shape formed by reducing the rectangular cross-sectional shape of the inner cells to obtain a reduced rectangle and chamfering or rounding two corners of the reduced rectangle, the cell partition walls include inter-peripheral-cell cell partition walls each located between the peripheral cells (21, 21a, 21b, 21c, 21d, 21e) and inter-inner-cell cell partition walls each located between the inner cells, and the minimum thickness of the inter-peripheral-cell cell partition walls is greater than the thickness of the inter-inner-cell cell partition walls,