An object is to provide an exhaust-gas purification device that is capable of uniformly mixing exhaust gas and a reduction agent together without being affected by the routing of an exhaust pipe of an internal combustion engine. An exhaust-gas purification device (1) includes an urea water injection nozzle (2) that is provided inside an exhaust pipe (14) and a catalyst reactor (12) that is provided on a downstream side of the urea water injection nozzle, and is configured to inject urea water from the urea water injection nozzle (2) into exhaust gas of an engine (18) and to reduce nitrogen oxide in the exhaust gas by a NOx catalyst (13) contained in the catalyst reactor (12), where the urea water injection nozzle is disposed in such a way as to inject the urea water from the axial center of the exhaust pipe toward the downstream side of the flow direction of the exhaust gas, and a mixer (11) is connected to an upstream end of the catalyst reactor, the mixer having a plurality of plate members (11b) radially disposed around the axial center of the exhaust pipe, the plate members each being formed in such a way that angles of plate surfaces (A, B) of the plate member to the flow direction of the exhaust gas are different values on the upstream side and the downstream side.