To use an easily recyclable material and to improve freedom of weight setting while strength is kept and to decrease cost.

A top board 1 consists of a surface board 7 made of a metal, an inner material 2, a back surface board 8 and decorative edge parts 10 and 10a and in the surface board 7, two sides are bent to form edge parts 6 and 6a and end edges 12 and 12a are extended to the back surface sides from the edge parts 6 and 6a and the inner material 2 is made into a folded board with top and bottom horizontal faces 3, 3a... and vertical faces 4, 4a... and the surface board 7, the top and bottom horizontal faces 3, 3a... of the inner material 2 and the back surface board 8 are stuck together and by fitting the decorative edge parts 10 and 10a into the opening parts of the two sides of the stuck surface board 7, the inner material 2 and the back surface board 8, while a necessary strength of the metal board being a main member of the top board 1 from which the decorative edge parts 10 and 10a can be separated is ensured, a required (the optimum) weight is set by adjusting the thickness, the area, etc., of the folded board 5, 5a... of the inner material 2 and by making the metal board to be a main material, cost is decreased and recycling properties are improved.