A honeycomb structure that carries a catalyst and serves as a heater when a voltage is applied thereto comprising: a pillar-shaped honeycomb structure body that includes a porous partition wall which defines and forms a plurality of cells formed as fluid flow passages and extending from a first end face as one end face to a second end face as the other end face, and that includes a circumferential wall located at an outer circumference of the honeycomb structure body; and a pair of electrodes which are disposed on a side surface of the honeycomb structure body, wherein an electric resistivity of the honeycomb structure body is 1 to 200 Ωcm, each of the pair of electrodes is formed in a band shape extending in an extending direction of the cells of the honeycomb structure body, in a cross-section orthogonal to the extending direction of the cells, one electrode of the pair of electrodes is disposed at the opposite side to the other electrode of the pair of electrodes with a center of the honeycomb structure body interposed therebetween, characterized in that an open frontal area of a center part is 0.70 to 0.95 times an open frontal area of an outer circumferential part, where the center part is defined as an area from a center of the honeycomb structure body to a position of 10% of a length from the center to the outer circumference in a direction toward the outer circumference in a cross-section orthogonal to the extending direction of the cells of the honeycomb structure body, and the outer circumferential part is defined as an area from the outer circumference to a position of 10% of a length from the outer circumference to the center in a direction toward the center in the cross-section. a pillar-shaped honeycomb structure body that includes a porous partition wall which defines and forms a plurality of cells formed as fluid flow passages and extending from a first end face as one end face to a second end face as the other end face, and that includes a circumferential wall located at an outer circumference of the honeycomb structure body; and a pair of electrodes which are disposed on a side surface of the honeycomb structure body, wherein an electric resistivity of the honeycomb structure body is 1 to 200 Ωcm, each of the pair of electrodes is formed in a band shape extending in an extending direction of the cells of the honeycomb structure body, in a cross-section orthogonal to the extending direction of the cells, one electrode of the pair of electrodes is disposed at the opposite side to the other electrode of the pair of electrodes with a center of the honeycomb structure body interposed therebetween, characterized in that an open frontal area of a center part is 0.70 to 0.95 times an open frontal area of an outer circumferential part, where the center part is defined as an area from a center of the honeycomb structure body to a position of 10% of a length from the center to the outer circumference in a direction toward the outer circumference in a cross-section orthogonal to the extending direction of the cells of the honeycomb structure body, and the outer circumferential part is defined as an area from the outer circumference to a position of 10% of a length from the outer circumference to the center in a direction toward the center in the cross-section.