In a system for specifying a lane marking deterioration, an image acquiring unit acquires a captured image of an outside of a vehicle. A specifying unit extracts a lane marking on a road surface included in the captured image and specifies a deteriorated portion of the lane marking. The specifying unit specifies the deteriorated portion of the lane marking in comparison with another lane marking included in the captured image. A receiving unit receives past lane marking data of a road included in the captured image. The specifying unit specifies, from the captured image, a deteriorated portion of the lane marking that has deteriorated from the past lane marking data.