Sound insulating floor structure and sound insulating floor composing material as well as method for reducing floor impacting sound

A sound insulating floor structure is formed by interposing an intermediate layer containing a buffering material made of a nonwoven fabric structure between a floor base material and a floor finish layer. A structure containing hygrothermally adhesive fibers and having fibers be fixed by fusion of the hygrothermally adhesive fibers is used as the nonwoven fabric structure. The sound insulating floor structure includes, for example, a floor base material 1, a buffering layer 2, a space layer 3, a hard layer 4 and a floor finish layer 5 stacked in sequence. In the structure, a supporting material 6 is interposed between the buffering layer 2 and the hard layer 4. The surface of supporting material may be 10 to 70% of the floor surface. By using the sound insulating floor structure, sinking of the floor caused by walking can be restricted, thereby obtaining a good walking feeling and excellent sound insulating properties against floor impacting sounds.