An exhaust gas treating device includes a honeycomb structure including an inner honeycomb structure body, an outer honeycomb structure body disposed at a position which surrounds a part of a circumference of the inner honeycomb structure body and is away from the inner inflow end face of the inner honeycomb structure body, and plugging portions arranged in parts of cells; a can member which stores the honeycomb structure and has an inlet and a second outlet for an exhaust gas; and an opening/closing valve to open and close the second outlet of the can member.