A road information detection device includes a curve-starting-position identification part configured to identify the starting position of a transition curve according to a road structure upon detecting an attached structure on a road. It further includes an image information capture part configured to capture an image, an attached-structure detection part configured to detect the identification of an attached structure reflected in the image, and a storage media configured to store the position of an attached structure. The curve-starting-position identification part may identify the starting position based on the detected identification of an attached structure, the stored position of an attached structure, and a distance from the attached structure to the starting position of a transition curve.