In aging societies, the number of walking disabilities, caused by stroke disease and paralysis or bone fracture, is increasing and in order to recover walking ability, rehabilitation is necessary. Currently a rehabilitation orthosis which fixes the knee movement to prevent buckling is used for severe patients, but this is not ideal rehabilitation since the muscle relies on the orthosis and does not need to support the weight of the body. Raplus is attached to a conventional rehabilitation orthosis, and assists movement of the knee. The device is light-weight and small not only because of exploiting a orthosis, but also because of supporting only 50% of the maximum force a knee can generate.