A honeycomb structure has a substantially circular-pillar-shape. The honeycomb structure includes at least one electrically conductive honeycomb unit, a first electrode, and a second electrode. The at least one electrically conductive honeycomb unit includes walls extending along a longitudinal direction of the at least one electrically conductive honeycomb unit to define a plurality of through holes. The first electrode is provided on an outer circumferential surface of the honeycomb structure. The second electrode is provided in a vicinity of a central axis of the honeycomb structure extending along the longitudinal direction.