PURPOSE: To reduce the rotational fluctuation in a short response time by providing each chamber wall with a drain hole communicating with an adjacent chamber, and charging the chamber with liquid of an amount capable of being distributed at the fixed rate to the volume of each chamber.

CONSTITUTION: At the time of stoppage of a flywheel 10, the liquid 7 inside a chamber fills in the chamber at the bottom of the flywheel passing through the drain hole 6 of each chamber, and upper chambers are vacant. When the flywheel 10 starts rotation, the liquid is scattered in each chamber by the centrifugal force, and during the rotation at constant velocity the liquid is distributed by equal quantities in each chamber, and the heights of the levels from the bottoms of the chambers become all equal. When the rotational fluctuation occurs in the flywheel, the liquid inside each chamber shifts in the direction opposite to the rotational fluctuation, and presses the wall 4 of each chamber in the direction opposite to the rotational fluctuation, and the rotational fluctuation is suppressed.