A urea water tank (23) is arranged in a cab (10) at which an operator boards, thereby making it possible to arrange urea water under a preferred temperature environment for preventing freeze and crystallization of the urea water. A water supply port (24A) is provided to be opened to a left surface portion (19C) of a cab box (19) constituting the cab (10) for supplying the urea water to the urea water tank (23) from an outside of the cab (10). Therefore, even in a case of resupplying the urea water to the urea water tank (23), an operator can easily resupply the urea water through a water supply hose (24) to the urea water tank (23) from the outside of the cab (10) without entering into the cab (10).