A mixing device includes: an elbow pipe attached to an outlet pipe of a filter device, the elbow pipe changing a flow direction of an exhaust gas flowing from the filter device; a straight pipe connected to a downstream side of the elbow pipe, the straight pipe extending in a direction intersecting an axial line of the outlet pipe; an injector attached to the elbow pipe and injecting a reductant aqueous solution inside the elbow pipe toward the straight pipe; and a mixing pipe disposed in the elbow pipe to serve as a cover for the reductant aqueous solution, the mixing pipe being provided with openings on a circumferential wall thereof. A cutout is provided at a fixing portion of the mixing pipe with the elbow pipe at a position for allowing the exhaust gas entering through an inlet of the elbow pipe to flow toward the injection nozzle.