Abstract: At least either of the upper and lower portions of each of a plurality of elastic bodies (30) provided between an upper structure (10) and a lower structure (20) is movable radially, simultaneously by the same distance in the longitudinal direction of the elastic bodies manually or by a driving means to change the position of an elastic center X, which exists in the axial direction of the machine body, and change the elastic force between the upper and lower structures (10, 20). Either of connections of each of the elastic bodies (30) to the upper and lower structures (10, 20) is a hinge joint or a spherical pair joint, and that of the other is a fixed joint.