PURPOSE: To suppress vibration in a small volume by storing a bulk material of the specific gravity of no less than one, in a tank, and by liquefying the bulk material, so as to make the natural frequency thereof in the tank identical with that of a structure.

CONSTITUTION: A vibration suppressing device 1 is installed on the roof of a structure, while a zircon sand 3 is stored in a tank 2, and a liquefying means 4 is provided. The liquefying means 4 is composed of a water storage tank 6 in which water 5 is stored, a feed pipe 7, and of a drainage pipe 9 provided with a pump 9. By generating the flow of an upward fluid on the gap of the zircon sand (bulk material), the bulk material is floated and is liquefied. By making the natural frequency of the liquefied bulk material and that of the structure identical, the vibration is suppressed. Since the specific gravity is defined not less than one, the volume is reduced compared with the case where the water is used as a fluid.