A honeycomb structural body has a honeycomb body and a pair of electrodes. 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 of the electrodes 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. The reference electrode parts of the electrode face to each other. The outside electrode parts of the electrodes face to each other. An electrical resistivity of the reference electrode part is smaller than an electrical resistivity of each of the outside electrode parts in each of the electrodes.