Abstract: A cylindrical honeycomb structure formed by spirally winding a strip metal flat sheet and a strip metal corrugated sheet overlapped thereon. The metal flat sheet is welded, at each turn, to the metal corrugated sheet at a plurality of axially arranged welding positions on each portion where the metal flat sheet contacts the metal corrugated sheet. Letting L be the axial length of the honeycomb structure and D be the diameter of the honeycomb structure, the maximum value L1 of distances between adjacent welding positions satisfies at least one of relationships given by L1≦/D/2 and L1≦/L/2, or the distance L2 between the outermost welding positions in the axial direction of the honeycomb structure and the outer end face of the honeycomb structure satisfies at least one of relationship given by L2≦/D/20 and L2≦/L/10.

Abstract: A cylindrical honeycomb structure 23 is formed by spirally winding a strip metal flat sheet 21 and a strip metal corrugated sheet 22 overlapped thereon while welding, for each turn, the metal flat sheet 21 to the metal corrugated sheet 22 at a plurality of welding positions W1 to W6 axially arranged on each of mutual contact portions of the metal flat sheet 21 and the metal corrugated sheet 22. Letting L be the axial length of the honeycomb structure 23 and D be the diameter of the honeycomb structure 23, the maximum value L1 of distances each between adjacent ones of the plurality of welding positions W1 to W6 satisfies at least one of relationships given by L1≦D/2 and L1 ≦L/2, or the distance L2 between the outermost one W1 or W6 of the plurality of the welding positions W1 to W6 in the axial direction of the honeycomb structure 23 and the outer end surface of the honeycomb structure 23 satisfies at least one of relationships given by L2≦D/20 and L2≦L/10.