In the first part of this study, theoretical and numerical evaluation of negative stiffness appearing in the skyhook control is conducted. The skyhook control is widely known for the vibration control method in the mechanical engineering field. The skyhook control can also achieve absolute response reduction. In order to realize a negative stiffness, however, the control force that accelerates the deformation should be generated. At present, such a performance is achieved only by using loading actuators or semi-active devices with sophisticated controllers and sensors. In the second part of this research, a new damper realizing a negative stiffness and stable energy dissipation in a passive manner is proposed, and its dynamic performance is investigated through large-scale shaking table tests. It is confirmed that the innovative negative stiffness passive damper reduces both the absolute acceleration and the relative displacement of a bridge model.