A data processing apparatus processes moving image data that shows a vicinity of a vehicle and that is recorded while the vehicle is running. The data processing apparatus includes a controller configured to: acquire behavioral information on a specific behavior of the vehicle during an image capturing period of the moving image data; acquire object information on an object in the vicinity of the vehicle during the image capturing period of the moving image data; and determine a cause of the specific behavior of the vehicle based on the behavioral information and the object information.