In recent years, many assist devices have been developing to enable the users to walk by an electric control system. However, introducing an electric control system makes the price rise of the device. It is difficult for users to purchase an expensive device, even if it is easy to use. In order to spread an assist device in daily life, a development with a low price and a simple device is expected. The device driven by external power sources disturbs users' independent action, there is a risk that it could be make users' physiologic function decline and users disincentive to do daily actions. An appropriate control system should be constructed in order to avoid an interference between a user's motion and a device's output motion. In case that the control system has the problem, an appropriate assisting motion can not be obtained, and it is in danger of harming to the user's body.So the design of devices is needed to consider for safety. The purpose of this research is the design and the development of a simple device for assisting walking motion which is driven by users' self, considering users' own physical condition. The assist device is designed by using a planar 6-link mechanism which transforms a rotational motion into an oscillating motion.The respective lengths of the links are determined by comparing the movement of the link, which the user's foot is put on, with the movement of the human leg in the action of walking. We optimize the device by using the Genetic algorithm while we consider the max value of input-torque to drive the device. In this study, the device assisting the user's legs are driven by the user's arm. Authors evaluate the device's supporting performance by the method of measuring the leg motion and the 1 南後 淳

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