PROBLEM TO BE SOLVED: To provide a urea water mixing structure which is high in versatility to a variety of types of exhaust emission control devices.SOLUTION: A urea water mixing structure comprises: a selective reduction type catalyst 4 which has a characteristic for making NOx selectively react with ammonia even under co-existence with oxygen, and is interposed in the middle of an exhaust passage 16; and an injector 8 (urea water adding means) for adding urea water into an exhaust gas 1 at the upstream side of the selective reduction type catalyst 4. In the urea water mixing structure, the urea water is added to and mixed with the exhaust gas 1 flowing in the exhaust passage 16 by the injector 8, a mixer 19 having a plurality of pieces of fins in a radial shape so as to form a swirl flow around an axial core O of the exhaust passage 16 is arranged between the injector 8 and the selective reduction type catalyst 4, and the urea water can be injected toward the mixer 19 from the injector 8.
