A honeycomb filter comprising: a plurality of cells for allowing exhaust gas to flow therethrough, the cells including exhaust gas introduction cells (12, 14) and exhaust gas emission cells, and porous cell walls defining rims of the plurality of cells, the exhaust gas introduction cells each having an open end at an exhaust gas introduction side and a plugged end at an exhaust gas emission side, the exhaust gas emission cells each having an open end at the exhaust gas emission side and a plugged end at the exhaust gas introduction side, the exhaust gas introduction cells and the exhaust gas emission cells each having a uniform cross sectional shape except for the plugged portion in a direction perpendicular to the longitudinal direction of the cells thoroughly from the end at the exhaust gas introduction side to the end at the exhaust gas emission side, the cell walls supporting an SCR catalyst, wherein each exhaust gas emission cell is adjacently surrounded fully by the exhaust gas introduction cells across the porous cell walls; the exhaust gas emission cells have a larger average cross sectional area than the exhaust gas introduction cells in a direction perpendicular to the longitudinal direction of the cells; the exhaust gas introduction cells have a larger total volume than the exhaust gas emission cells; the exhaust gas introduction cells include first exhaust gas introduction cells and second exhaust gas introduction cells each having a larger cross sectional area than each first exhaust gas introduction cell in a direction perpendicular to the longitudinal direction of the cells; each exhaust gas emission cell has a cross sectional area equal in size to each second exhaust gas introduction cell in a direction perpendicular to the longitudinal direction of the cells; and in the cross section perpendicular to the longitudinal direction of the cells the exhaust gas introduction cells and the exhaust gas emission cells are each polygonal, and a side forming the cross sectional shape of each first exhaust gas introduction cell faces one of the exhaust gas emission cells, a side forming the cross sectional shape of each second exhaust gas introduction cell faces one of the exhaust gas emission cells, and the side of the first exhaust gas introduction cell is longer than the side of the second exhaust gas introduction cell, wherein, in the cross section perpendicular to the longitudinal direction of the cells, the exhaust gas emission cells are each octagonal, the first exhaust gas introduction cells are each square, and the second exhaust gas introduction cells are each octagonal. a plurality of cells for allowing exhaust gas to flow therethrough, the cells including exhaust gas introduction cells (12, 14) and exhaust gas emission cells, and porous cell walls defining rims of the plurality of cells, the exhaust gas introduction cells each having an open end at an exhaust gas introduction side and a plugged end at an exhaust gas emission side, the exhaust gas emission cells each having an open end at the exhaust gas emission side and a plugged end at the exhaust gas introduction side, the exhaust gas introduction cells and the exhaust gas emission cells each having a uniform cross sectional shape except for the plugged portion in a direction perpendicular to the longitudinal direction of the cells thoroughly from the end at the exhaust gas introduction side to the end at the exhaust gas emission side, the cell walls supporting an SCR catalyst, wherein each exhaust gas emission cell is adjacently surrounded fully by the exhaust gas introduction cells across the porous cell walls; the exhaust gas emission cells have a larger average cross sectional area than the exhaust gas introduction cells in a direction perpendicular to the longitudinal direction of the cells; the exhaust gas introduction cells have a larger total volume than the exhaust gas emission cells; the exhaust gas introduction cells include first exhaust gas introduction cells and second exhaust gas introduction cells each having a larger cross sectional area than each first exhaust gas introduction cell in a direction perpendicular to the longitudinal direction of the cells; each exhaust gas emission cell has a cross sectional area equal in size to each second exhaust gas introduction cell in a direction perpendicular to the longitudinal direction of the cells; and in the cross section perpendicular to the longitudinal direction of the cells the exhaust gas introduction cells and the exhaust gas emission cells are each polygonal, and a side forming the cross sectional shape of each first exhaust gas introduction cell faces one of the exhaust gas emission cells, a side forming the cross sectional shape of each second exhaust gas introduction cell faces one of the exhaust gas emission cells, and the side of the first exhaust gas introduction cell is longer than the side of the second exhaust gas introduction cell, wherein, in the cross section perpendicular to the longitudinal direction of the cells, the exhaust gas emission cells are each octagonal, the first exhaust gas introduction cells are each square, and the second exhaust gas introduction cells are each octagonal.