To facilitate the preparation of lanes, by pivotting a cover and a curb at both side walls of a side drain so as to freely develop them outward and rise and fall.

A cover (a) provided with nearly a half of width of the upper opening of a side drain A and a flat surface and support legs 3 at the rear face is fitted to the upper part of one side wall 4 of the side drain A so as to be freely developed. A curb (b) with a U-shaped section having standard dimensions is fitted to the upper part of the other side wall 6 of the side drain A so as to be freely developed and a mounting member 7 which can be placed on the cover (a), is fixed to a specified position of the curb (b). Then, when lanes are prepared, the mounting member 7 is placed on the upper face of the cover (a) and the curb (b) is erected. When a field is prepared, the curb (b) is turned down and the mounting member 7 is contained in the side drain A in the state it is folded close to the inside face of the side wall 6. And further, when cleaning the inside of the side drain, the cover (a) and the curb (b) are unfolded outward to remove foreign materials in the side drain A. In this way, the lane and the field can be easily and rapidly prepared.