A honeycomb filter includes a pillar-shaped honeycomb substrate including a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face, an inflow side plugging portion disposed at the inflow end face of the honeycomb substrate to plug open ends of outflow cells; and an outflow side plugging portion disposed at the outflow end face of the honeycomb substrate to plug open ends of inflow cells other than the outflow cells. The honeycomb substrate includes the partition wall that defines two of the inflow cells by division. An average of the plugging length L.sub.OUT of the outflow side plugging portions disposed in the inflow cells of the honeycomb substrate is larger than an average of the plugging length L.sub.IN of the inflow side plugging portions disposed in the outflow cells of the honeycomb substrate.

An exhaust gas purifying device includes: a columnar honeycomb carrier provided in an exhaust channel; a tubular case member housing the honeycomb carrier; and a retaining member surrounding the outer circumference of the honeycomb carrier. The honeycomb carrier has, in the outer circumferential edge of an inlet-side end face and an outlet-side end face, respectively, sloped surfaces sloped toward a direction in which the length in the center axis direction of the honeycomb carrier decreases. Of the retaining member, ends in the center axis direction of the honeycomb carrier extend to the sloped surfaces of the honeycomb carrier, and the ends have tapered parts which are longer in the center axis direction of the honeycomb carrier on the side facing the case member than on the side facing the honeycomb carrier.

A honeycomb formed body containing a ceramics raw material, he honeycomb formed body including: a pillar shaped honeycomb structure portion having a plurality of rectangular cells, the cells being defined by partition walls and extending from a first end face to a second end face to form flow paths; an outer peripheral portion having outer peripheral portions X where the partition walls are covered with an outer peripheral wall; and outer peripheral portions Y where the partition walls are exposed. Each of the outer peripheral portions X includes a tapered portion having a gradually deceasing thickness of the outer peripheral wall toward a boundary portion with an adjacent outer peripheral portion Y. The tapered portion requires a length equal to or more than one time of an average cell pitch in the outer peripheral direction until thickness of the outer peripheral wall is halved.

A honeycomb structure including a honeycomb portion having porous partition walls extending from an inflow end face to an outflow end face, an outermost peripheral wall, and a pair of electrode layers on a side surface of the honeycomb portion. Each electrode layer extends in a direction of the cells. One electrode layer is disposed on a side opposite to the other electrode layer across a center of the honeycomb portion in a cross section orthogonal to the extending direction of the cells. The honeycomb structure portion includes first cells opened on the inflow side and plugged on the outflow side, and second cells opened on the outflow side and plugged on the inflow side. A middle of each length of the pair of electrode layers is closer to the outflow side than a middle position of a length of the honeycomb portion in the extending direction of the cells.

A honeycomb filter includes a honeycomb structure including a porous partition wall surrounding cells, porous inflow side plugging portions and porous outflow side plugging portions. Each inflow side plugging portion includes, on an inflow side, a low porosity part having a porosity P1(%) of 70% or less and includes, on an outflow side, a high porosity part having a higher porosity than the low porosity part. The high porosity part has a porosity P2(%) satisfying P2(0.8904P3)+(0.7716N1)37.585, where P3(%) represents a porosity (%) of the partition wall; and N1(%) represents an open frontal area (%) of the cells, and the high porosity part has a length of 1 mm or more.

The honeycomb structure is equipped with a pillar-shaped honeycomb structure body having a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face and serving as a through channel of a fluid and a circumferential wall placed to surround the circumference of the partition wall. The honeycomb structure body has, in a face orthogonal to an extending direction of the cells of the honeycomb structure body, a circumferential cell structure, a center cell structure, and a boundary wall placed at a boundary between the circumferential cell structure and the center cell structure and incomplete cells of 5% or more to 50% or less of the total number of the incomplete cells of the center cell structure is communicated with incomplete cells of the circumferential cell structure with each other.

A honeycomb filter including: a pillar-shaped honeycomb structure including porous partition walls; and porous plugging portions disposed on either one of end portions of each of the cells, wherein a porosity (%) of the partition walls is defined as P1, a porosity (%) of the plugging portions is defined as P2, an occupancy (%) of the partition walls relative to an area of a cross section orthogonal to an extending direction of the cells of the honeycomb structure is defined as N1, the P1 is 50 to 65%, the P2 is 60 to 70%, the N1 is 22 to 39%, and X represented by Formula (1) satisfies a relation of Formula (2):

X=P1/P2N1,Formula (1):

18.800.19X.sup.2+11.33X121.6350.50.Formula (2):

A honeycomb filter includes a pillar-shaped honeycomb structure body having a porous partition wall surrounding cells each of which has one end plugged by a plugging portion. An open frontal area O (%) of the cells in the honeycomb structure body is 75 to 80%, a porosity P (%) of the partition wall measured by a mercury press-in method is 52 to 58%, an average pore diameter D (m) of the partition wall measured by the mercury press-in method is 6 to 12 m, and a pore volume rate A (%) of pores whose pore diameters are not less than 20 m with respect to an overall pore volume of the partition wall is not more than 13.5%.

The honeycomb structure includes a pillar-shaped honeycomb structure body that includes a porous partition wall. When the thickness (m) of the partition wall is defined as T.sub.1 and, among pores formed in the partition wall, the value of an average pore diameter (m) of specific pores whose pore diameters measured by a mercury press-in method are 20 to 100 m is defined as D.sub.(20 to 100), T.sub.1/D.sub.(20 to 100) that is a value obtained by dividing T.sub.1 by D.sub.(20 to 100) is not less than 2.4, a ratio of a pore volume of the specific pores to an overall pore volume of the partition wall is 5 to 45%, and a ratio of a pore volume of large pores whose pore diameters are not less than 100 m to the overall pore volume of the partition wall is not more than 5%.

A honeycomb structure, including: a pillar-shaped honeycomb structure body having a first end face and a second end face and including a porous partition wall disposed so as to surround a plurality of cells, the plurality of cells extending from the first end face to the second end face and serving as a through channel of fluid, wherein the partition wall has a porosity of 45 to 65%, the partition wall has an average pore diameter of 15 to 25 m, and the partition wall has a cumulative pore volume, which is measured by mercury intrusion porosimetry, such that a pore volume ratio of pores having pore diameters of 10 m or less relative to the overall pore volume of the partition wall is 10% or less, and a pore volume ratio of pores having pore diameters of 40 m or more is 10% or less.