PURPOSE: To prevent the damage of a cabin when a front loader is attached and detached, by a method wherein a small window is formed in a front wall part, facing a position where a control valve is located, of a tractor cabin, and a control lever for the valve passes through and emerges from the small window.

CONSTITUTION: A control valve 12 for controlling a front loader 1 is mounted to a rear surface of an attaching member 8 of the front loader 1 installed to a tractor. A control lever 13 for the control valve 12 is positioned so that it projects into a cabin 2 from the front wall surface of the cabin 2. A window 15 for observing a side of a tractor body is formed in the front wall part of the cabin 2, a clear resin plate 16 is fitted in the window 15, and a small window 17 is formed by partially notching the plate 16. The small window 17 is covered with a clear plate 18 having an aperture 18a, a tubular connecting rod 19, being connected to an original control lever 12a for the valve 12, loosely engages the aperture 18a, and the connecting rod 19 acts as the extension part of the control lever 13.