A honeycomb structure comprising: a pillar honeycomb structure body having porous partition walls defining a plurality of cells which become through channels for a fluid and extend from a first end face to a second end face, and a circumferential wall positioned at an outermost circumference; and a pair of electrode members disposed on a side surface of the honeycomb structure body, wherein the honeycomb structure body heats by energization, each of the pair of electrode members is shaped in the form of a band extending in an extending direction of the cells of the honeycomb structure body, in a cross section perpendicular to the extending direction of the cells, one electrode member in the pair of electrode members is disposed on a side opposite to the other electrode member in the pair of electrode members via a center of the honeycomb structure body, one or more slits opened in the side surface are formed in the honeycomb structure body, the honeycomb structure body has a charging material charged into the at least one slit, the charging material is disposed in at least a part of a space of the slit, the charging material contains aggregate particles and a neck material, the neck material being located in spaces between the aggregate particles to bond and fix the aggregate particles to one another, and a ratio (α2/α1) of a thermal expansion coefficient α2 of the charging material at 25 to 800°C to a thermal expansion coefficient α1 of the honeycomb structure body at 25 to 800°C is from 0.6 to 1.5, characterized in that the charging material contains 5 to 25 mass% of the neck material, and wherein the aggregates contained in the charging material include cordierite, the mass% of the aggregates including cordierite in the charging material being 50 mass% or more. a pillar honeycomb structure body having porous partition walls defining a plurality of cells which become through channels for a fluid and extend from a first end face to a second end face, and a circumferential wall positioned at an outermost circumference; and a pair of electrode members disposed on a side surface of the honeycomb structure body, wherein the honeycomb structure body heats by energization, each of the pair of electrode members is shaped in the form of a band extending in an extending direction of the cells of the honeycomb structure body, in a cross section perpendicular to the extending direction of the cells, one electrode member in the pair of electrode members is disposed on a side opposite to the other electrode member in the pair of electrode members via a center of the honeycomb structure body, one or more slits opened in the side surface are formed in the honeycomb structure body, the honeycomb structure body has a charging material charged into the at least one slit, the charging material is disposed in at least a part of a space of the slit, the charging material contains aggregate particles and a neck material, the neck material being located in spaces between the aggregate particles to bond and fix the aggregate particles to one another, and a ratio (α2/α1) of a thermal expansion coefficient α2 of the charging material at 25 to 800°C to a thermal expansion coefficient α1 of the honeycomb structure body at 25 to 800°C is from 0.6 to 1.5, characterized in that the charging material contains 5 to 25 mass% of the neck material, and wherein the aggregates contained in the charging material include cordierite, the mass% of the aggregates including cordierite in the charging material being 50 mass% or more.