To improve recognition accuracy of a traveling direction of a vehicle by accurately detecting a marking on a road surface which is photographed by a camera while a road environment where a vehicle travels is changing. A car navigation system 100 detects an image of a light-irradiated portion which is unnecessary for the recognition of a road marking, in an image behind a vehicle captured by a camera 6 mounted on the vehicle, clips out image areas in a predetermined shape excluding the detected image area, and sequentially stores the clipped images in a storage unit 7b. Then, the new clipped image and the clipped image already stored in the storage unit 7b are combined, and an image of a road marking is detected and recognized from the composite image.