In recent years, there have been many bed-ridden people because of Cerebral accidents for elderly people in Japan. Almost of them have problem of their joints, which is known for contracture. In this condition, they cannot move their hand's fingers smoothly. If the symptom occurs for the hand's fingers, patients have difficulties to live independently. Then, physical therapists (PT) take an important part in improvement and prevention for the patient's disability. However, PT has to do rehabilitation training multiple times in a day. Accordingly, they not have much time to train many patients. For these reasons, patients cannot get appropriate training when they need. Therefore, this study was made to develop the contracture prevention device for the finger joints. In this paper, we described the prototype for index finger of our device. It consists from cam and link mechanisms by using a DC motor. Furthermore, we examined extension degree and force exerted to finger joints. For these experiments, we indicated this prototype can extend the index finger joints automatically and transitivity.