a hinge rubber or plastic etc which functions as a hinge joint so that the cover panel 2 can be raised and lowered the cover panel 2 is provided with a rear windshield 5 at its rear portion and forms an integral roof cover plate of the cabin together with the rear windshield 5 so as to be raised and lowered simultaneously an extendable and retractable enclosure plate 4 is provided under the roof cover plate and the lower end of the extendable and retractable enclosure plate 4 is connected with the surrounding border of the cabin to form a sealed cabin the cabin roof cover plate can be lowered onto the surrounding border of the cabin by pressing the extendable and retractable enclosure plate 4 the extendable and retractable enclosure plate 4 may be made of plastic rubber canvas or corrugated plate etc as shown in fig1 the extendable and retractable enclosure plate 4 is a corrugated plate which can extend and retract in the up and down direction so that the cabin roof cover plate can be raised or lowered the backward slope of the door frames 3 can be large the rear portion of the door frames 3 can be much lower than the front portion such configuration contributes to the faster.