To reduce the vibration of a structure by an earthquake with a simple construction by mounting a cushioning oil damper formed of a flange, a cylinder, a pressing plate and the like only on one of juxtaposed structures.

A cushioning oil damper 22 formed of a flange 4, a cylinder 7, a pressing plate 12 and the like is mounted only on one structure A of juxtaosed structures A, B by an anchor bolt 5. Then, when both the structures A, B mutually approach by a vibration such as earthquake, the cushioning oil damper 22 presses the matching structure B to exhibit a damping effect. When both the structures are mutually isolated by the vibration, no damping effect is exhibited. The vibration by the earthquake can be reduced with a simple construction without requiring anchoring of both the adjacent structures A, B. This method can be also effectively applied to the vibration prevention of a building equipment or furniture.