PROBLEM TO BE SOLVED: To supply urea water from a urea water tank appropriately by suppressing the precipitation of a urea crystal in the urea water tank. SOLUTION: A DPF 12 and an SCR catalyst 13 are arranged in an exhaust conduit 11, and between the DPF 12 and the SCR catalyst 13, a urea water adding valve 15 for adding and supplying the urea water in the exhaust conduit 11 is arranged. To the urea water adding valve 15, the urea water tank 21 is connected via a urea water supplying pipe 23. Moreover, to the urea water tank 21, a water supplying tank 41 is connected via water supplying piping 43, and water is appropriately supplied to the urea water tank 21 from a water supplying pump 42. COPYRIGHT: (C)2010,JPO&INPIT