The wave absorbing control using wave sensors was theorized and developed by the authors, about 30 years ago. It was originally for absorbing wavemakers for tank tests in laboratories. This control enables wavemakers to generate the desired incident waves while absorbing undesirable reflected waves from the tank wall. When waves are absorbed by the wavemaker, the energy of the waves are also absorbed, that is, the energy is regenerated to electric power with the wavemaker drivemotor. According to this theory, in case that certain waves are generated by an oscillating body, these waves can be absorbed by the same body. Therefore, we can design a wave energy converter as a kind of absorbing wavemaker.