To restrain the vibration of a structure by adjusting the period (natural frequency) for moving the liquid in a vibration damping tank and matching with the vibration frequency of the structure installing the tank for restraining vibration, in the tank applied to the vibration prevention of a high building and a tower shape structure.

Vertical tanks 2, 2 installed in parallel therewith are arranged on the right/left sides of an U-shaped communication tank 1 and liquid 3 is filled in respective tanks 1, 2. The inside of the vertical tank 2, 2 is divided and partitioned in a vertical direction by a partition plate 4 more than one and a sluice valve 5 is installed on the sunk position of the liquid 3 in respective partitions. The movement of the liquid in the vertical tank 2 is closed partially by the sluice valve 5 and the tank is constituted so that the rate between the area for moving the liquid in the vertical tank and the area for moving the liquid in the tank in a horizontal direction can be changed. Thereby, natural frequency can be adjusted.