The honeycomb structure body has a dense part at a part in axial direction including a center region of the inflow end face, the dense part having a change ratio of porosity calculated by the following Expression (1) that is 2 to 8%, and has an outside-diameter increasing part, and the honeycomb structure body has a change ratio of average diameter calculated by the following Expression (2) that is 0.2 to 3%, (1−Px/Py)×100, Expression (1): in Expression (1), Px denotes the porosity (%) at the center region of the inflow end face, and Py denotes the porosity (%) of a circumferential region of the inflow end face. (1−Dx/Dy)×100,   Expression (2): in Expression (2), Dx denotes the average diameter (mm) of the inflow end face, and Dy denotes the average diameter (mm) of the outflow end face.