A first circumferential wall disposed in a circumference of partition walls has no interface with the outermost circumference partition wall in a circumferential portion constituted by the partition walls whose wall thickness is larger than that of a central portion constituted by the partition walls in a central region. A maximum thickness of a total of the first circumferential wall and a second circumferential wall disposed to surround an outer side of the first circumferential wall is 1.2-3.0 mm, a difference between the maximum thickness and a minimum thickness of the total is 0.2-1.5 mm, and there is satisfied a relation, 0.5≤(TB−TA)×SB/SA×100(%)≤9.0 in which TB and TA indicate average thicknesses (μm) of the partition walls in the circumferential and central portion respectively, and SB and SA indicate areas (cm2) of the circumferential portion and the honeycomb structure in the cross section respectively.