To reduce impulsive sound of a floor by suspending a ceiling material from a ceiling substrate through a sound insulation unit in which a plate and an energy absorbing member are arranged in a prescribed state.

A ceiling material 2 is suspended from a ceiling substrate 1 through a plurality of sound insulation units 6, the periphery of the unit 6 that is close to a wall material W integral with the substrate 1 is supported to the wall W by an elastic body 8. Subsequently, in the unit 6, a plurality of closed small spaces S are formed of partition plates 4A and 4B parallel with the substrate 1 and the ceiling material 2, vertically elastically deformable energy absorbing members 5A and 5B made up of an elastic rubber and a metal bellows, whereby propagation downstairs of the impulsive sound of a ceiling through a solid propagation route can be reduced due to the consumption of vibration energy by the vibration of the entire sound insulation units due to the elastic displacement of the energy absorbing members, and the vibration of the partition plate consumes vibration energy and reduce propagation through an air propagation route. An air propagation sound from a wall material also can be reduced by the consumption of vibration energy by the small spaces.