Patent ID: 7897237

Claim:
A tubular honeycomb structure comprising partition walls which define and form a plurality of cells each functioning as a fluid passage extending from a first end face of the honeycomb structure to a second end face, wherein areas of sections of the individual cells (cell sections) normal to a flow direction of fluid are made so as to be approximately equal to each other over a given range of a center of each cell and a vicinity of the center of each cell in the fluid flow direction and to gradually decrease or gradually increase at each cell end of at least one end face of the honeycomb structure in the fluid flow direction, wherein an outer diameter of the honeycomb structure at least at one end face of the honeycomb structure is made so as to gradually decrease or gradually increase by more than ±0.5% of an outer diameter of the honeycomb structure at a center of the honey comb structure and a vicinity of the center of the honeycomb structure.