In a lane marker detection system, an image capturing element captures a road image ahead of a vehicle. The road image contains a plurality of color light components individually extractable therefrom. A selecting element extracts color groups from at least one of left and right areas of the road image in front of the vehicle, and selects, from the extracted color groups, one color group. The color groups are comprised of one or more combinations of at least one of the plurality of color light components. The selected one color group has a position in the at least one of the left area and the right area with a contrast equal to or higher than a threshold. The position of the selected one color group is the closest to a boundary between the left and right areas in the extracted color groups.