Recognition of circular road signs in road images was investigated. Detecting the road signs in the image using color information is difficult, because it is easily influenced by several conditions like whether. We used the shape of road signs instead. It is not influenced by above conditions. Hough transform for circle detection was used. It adapts to the various size of circle and scratchy edge well. Using the table of circumference coordinates, the detection was accelerated. 194 road images taken by the video camera placed at passenger seat were used for evaluation. The detection rate of 82.6% and the recognition rate of 76.9% were obtained.
