PURPOSE: To prevent floor materials from rising caused by their extension by intervening spacers having a thickness corresponding to the quantity of extension caused by water containing in the width direction of ligneous series floor material and fixing them and removing them before the adhesives are dried and cured.

CONSTITUTION: A sound insulation floor plate 2 is formed by providing a cushion layer 1 comprising urethane resin in the back face and recessed section of a substance comprising many ligneous strips of abut or solid plates 5 of abutted on each other. An convex section 6 is formed on the longitudinal direction side of the sound insulation floor plate 2, and a recessed section 7 is formed on the other side. Parts resulting from being cut at cutting lines L are stuck and fixed to he floor backing, and the convex section 6 of the ligneous series floor material 2 adjacent thereto in the backward direction is processed in the longitudinal direction so as to connect to the recessed section 7. In the next step, with a plurality of spacers 4 having substantial quantity of extension caused by containing water therein in the width direction of this floor material 2 intervened, ligneous series floor materials 2 and 2 are laid and fixed in the width direction to remove the spacers 4 before adhesives is dried and cured. By this constitution the rising of the ligneous series floor material due to the increase in moisture percentage can be prevented.