PURPOSE: To damp vibration of a structure by a method in which the force of holding the rope of a clamp actuator built in a second weight is adjusted, and a first weight connected to the rope is moved in the right and left directions on the structure.

CONSTITUTION: When the ground 2 is vibrated by earthquake, the force of holding the rope 7 of a clamp actuator 8 is loosened by the detected signals of a vibration sensor 10 in a control circuit 9. At the same time as a second weight 5 beings to lower, the tension of the rope 7 is lowered and a first weight 3 is accelerated to the right direction by the tension of an expandable spring 4. The detection signal of the sensor 10 is then varied, the signal of the circuit 9 is varied, and the force of holding the rope 7 of the actuator 8 is increased. Whereupon, the lowering speed of the weight 5 is reduced, the tension of the rope 7 is increased, and the weight 3 is accelerated to the left direction.