An exhaust gas purifying device for an internal combustion engine includes an inflow case provided with an inlet pipe, a catalyst case in which an oxidizing catalyst for dosing is housed, a filter case in which a soot filter is housed, and an outflow case provided with an outlet pipe, and is attached to an attached target at two attachment points mutually spaced in the axial direction of the cases. At one of the two attachment points, which is defined on the catalyst case, the catalyst case is firmly fixed. At the other attachment point, which is defined on the filter case, the filter case is attached slidably in the axial direction.