The purpose of this study is to develop a device for preventing a misstep, which causes serious injuries. In this study, a wearable walking assist device to support them is developed. Their walk speed and step can be improved by supporting a flexing action of hip joint. To support walking safely and smoothly. The device is required to have a lightweight and simple structure. Therefore a pneumatic rubber artificial muscle which has a lightweight and high power-weight ratio is used as an actuator. In this paper, the structure and characteristic of this device is described. Additionally, the effectiveness of this device is evaluated experimentally.