PURPOSE: To execute work in a short time by layering an old platform with a pavement material layer to be a floor surface on a hard urethane foam layer formed by foaming at site.

CONSTITUTION: An L type bracket 41 is fixed on a surface on an old platform 1 by an anchor bolt 43. Next, a fringe end plate 4 is fixed by a bolt 42 in a rising part of the L type bracket 4. Then, a layer 2 of hard urethane foam having density of 20 to 70kg/m3 is formed by a spray foaming method or a froth foaming method in a section surrounded by the surface of the old platform 1 and the fringe end plate 4. A meshlike reinforcing member 51 is put on a top face of the hard urethane foam layer 2. Furthermore, a waterproof layer 5 is formed by an ultra speed hardening urethane film waterproof spray on a top face of the meshlike reinforcing member 51. Then, a layer 3 of asphalt pavement material is formed on a top face of the waterproof layer 5.