Located in front of the revolving frame 5 is formed on the engine 8 at the same time installing the hydraulic fluid tank 15, situated in front of the working oil tank 15 is disposed the fuel tank 16. In the lower side of the fuel tank 16, a portion of the swing cylinder 14 so that it rests install the mounting member (17). The working oil tank 15 and is between the mounting member 17, a fuel tank 16, the forward and rear direction and vertically to restrict upward and downward bound port 20, and a left direction and a right fuel tank 16 It is detachably attached to the horizontal constraining opening (25) for restricting a direction. Owing to this arrangement, the fuel tank 16 can be constrained in two directions of the horizontal direction and the vertical direction.