As average age goes up, the lack of young workers and the subsequent increase of hard work by elderly and weak young people are becoming social problems in Japan. We have been developing a wearable power assist suit as labor-reducing equipment for such elderly and young workers. It is necessary to detect wearer's intention and predict following motion because the power assist suit is required to move simultaneously with the wearer. We propose the method of estimation of walking intention without using bioelectrical signals such as surface electromyogram signals, which usually have inferior S/N ratio. We estimate walking intention using the on-off signal of foot switches and hip joint angles. As a result of the experiment of walking on a model course including flat ground and stairs, accurate walking intention estimation was confirmed.