1. A marker generation device in which feature points extracted from an image are arranged in a predetermined space, and portions of this predetermine space in which the number of said feature points is equal to or less than a predetermined number are defined as unique features, comprising: a feature comparator that arranges the feature points extracted from an identifier in the predetermined space, and counts the number of the feature points matching with said unique features; and a marker pattern generator that converts a configuration of said identifier, and extracts said feature points from this identifier subjected to the conversion, wherein said feature comparator arranges the feature points extracted from said identifier subjected to the conversion in said predetermined space, counts the number of the feature points matching with said unique features, and selects as a detection marker the identifier of which said count number is most numerous, out of the identifier not subjected to the conversion and one identifier subjected to the conversion, or two or more.