A honeycomb structure according to the present invention has partition walls, and a number of through-holes divided from each other by the partition walls and extending in an axial direction. The honeycomb structure contains silicon carbide (SiC) or a composite material having silicon carbide (SiC) as a main crystal phase, and has a cylindrical shape. A circularity of a periphery of the honeycomb structure is in a range of 1.0 to 2.5 mm. The honeycomb structure can be contained in a metal container in stable state and hardly has problems such as breakage or breakdown.