To newly install a forest road at the height capable of securing the sight distance suitable for the traffic of vehicles and facilitate the execution at a low cost.

The natural ground 1 is cut off, a pit excavation sufficient to form a surefooting gutter Al is applied at a shoulder, a foundation 4 is installed, and a side ditch member 5a provided with an erect wall 7 on a concrete ditch section 6 is arranged in a pit excavation section 3 so that the erect wall 7 is located on the ridge side. A retaining wall 8a formed with wooden columns 9 extended upward from the erect wall 7 and horizontal bars 10 into a fence shape is installed in contact with the erect wall 7 in the pit excavation section 3, and back filling is applied to the pit excavation section 3 to the height of the retaining wall 8a.