In this paper, we propose a method of white line detection on a road. Most conventional techniques of white line detection use methods of line detection by a Hough transform and extraction using the luminosity of the white line. These techniques have problems because the detection is affected by sunlight conditions and texture of the road. We focus on the luminosity distribution around a white line since the surrounding distribution is relatively darker than the white line. We designed a double circular operator that can extract the features of the white line. By using this operator, our method can extract the white line of a specified width at a low calculation cost, even when a shadow or occlusion exists on the white line and the texture of the road surface is not smooth.