To secure excellent load bearing performance while highly securing sound insulation performance in a dry type sound insulation double floor.

A vibration isolating rubber 1 is formed to be a deformed rhombic cylinder so that the area of the top and the bottom faces may be the same. By receiving impulsive vibrations, being applied to the truncated top face, by the small area, the amount of energy transmission is suppressed. The isolating rubber is made to be rhombic cylinder to increase the volume of the rubber to increase the amount of attenuation and absorption of the energy, and the amount of energy transmission to a lower skeleton slab is reduced because of the small area. A cylindrical boring 3 for shape retaining, which is formed vertically in the isolating rubber at its center, has an outwardly recessed surface 2 so that the compression or expansion of the isolating rubber resulting from the floor load may be prevented. Further, the excellent shape retaining performance enables the hardness of the isolating rubber to be lowered to 63° or less to enhance the vibration isolating performance.