This study presents an Active Wheel Damper (AWD) unit that can be easily mounted on flexible structures such as cantilever beams. The AWD uses a gyro sensor to directly measure the absolute angular velocity, which is the rotational velocity of the slope angle of a deflection curve caused by the flexible vibration of the structure, and can be used to realize a skyhook control by the direct feedback of the angular velocity. This study proposes a Sky-hook With Adaptive Disturbance Cancellation (SWADC) control—which is constructed as a combined skyhook control and an adaptive disturbance cancellation control system—to enhance the capability of the AWD unit to suppress vibrations. An adaptive algorithm, which estimates the frequency of vibration of a structure in real time, is derived on the basis of an adaptive notch filter algorithm. The estimated frequency is used to model a disturbance observer that estimates harmonic disturbances. This study demonstrates the vibration-suppression performance of the AWD unit by numerical simulations and experiments.