To remarkably improve a sound insulating performance by a method wherein a dynamic spring constant is made smaller by remarkably reducing an air spring constant without increasing the weight of a material.

At the surface of this sound insulating material, a porous space as the way of escape of the air is provided. A second sound absorbing material layer 12 provided as the porous space has the preferable average fiber diameter of 5 denier or more, the preferable average apparent density of 0.005-0.1 g/cm3 and the preferable thickness of 1-50 mm. In order to most efficiently exhibit the reduction effect of an air spring, the porous space (the second sound absorbing material layer 12) is desirable to be provided on both the sides of a sound absorbing material (a first sound absorbing material layer 11).