Visually impaired people are limited in movement both indoors and outdoors. To solve this problem, existing studies propose a navigation system that leads visually impaired people on the route to their destination by detecting obstacles on the route and tracking their position using information and communication technology. Visually impaired people recognize their position and the route to their destination by combining these positioning methods. On other hand, existing studies propose detection of obstacles by image processing, but this method take a long time. Hence, we have proposed the high-speed detection of a down staircase for visually impaired people. The proposed method quickly detects the boundary line between the down staircase and floors using the illuminance of a point pattern. Moreover, the proposed method recognizes the down staircase quickly because it removes images that are clearly different from the down staircase and applies image processing to the pedestrian route only. Experimental results have shown that the proposed method can recognize a down staircase and border line with more than 90% accuracy. As a result, visually impaired people can safely go down a flight of stairs using this method.