In this paper, the authors developed a vibration control device (V.C.D.) using a power generator and a flywheel which is suitable for vibration suppression of a structure. The V.C.D. consists of a ball screw, a ball nut, a flywheel, a gear, and a power generator. The linear motion is converted into a rotating motion by the ball screw mechanism. The damping force is generated by the power generator, and controlled by an electric resistance at the terminal of the power generator. The inertial force is created by the flywheel which is attached to the end of the screw shaft. Since these forces are magnified by the ball screw and the gear, the V.C.D. has resisting force characteristics as the sum of the controllable damping force and the inertial force in the low frequency range. In order to investigate dynamic properties, a test V.C.D. is manufactured, and the resisting force characteristics are measured by using a vibration actuator. The experiments of frequency response are carried out using a shaking table, and the experimental results are compared with the theoretical results. The seismic responses are calculated under a semiactive control based on Linear Quadratic Regulator, and the effects of the vibration suppression of the V.C.D. are discussed experimentally and numerically.