A honeycomb structural body has a honeycomb body and an electrode pair. The honeycomb body has a cell formation part and an outer skin part of a cylindrical-hollow shape. The electrodes are formed on an outer peripheral surface of the outer skin part so that the electrodes face to each other in a diameter direction of the honeycomb body. Each electrode has a reference electrode part formed at a central part of the electrode and one or more outside electrode parts formed at both ends of the reference electrode part. An electrode terminal is formed at the central part of each electrode. The reference electrode parts of the electrodes face to each other. The outside electrode parts of the electrodes face to each other. A thickness of each electrode is gradually decreased from the central part toward the outside of the electrode along the circumferential direction of the honeycomb body.