An index arranged on a real space is detected from an image sensed by a camera, and the position of the index in the image is calculated (S405). The index is projected onto the image sensing plane of the camera on the basis of the position and orientation information of the camera, the position information of the index, and the like (S403). A corresponding index is identified based on the distance between the detected and projected indices on the image plane, and geometric information of the index (e.g., directionality) (S408). With this method, an index can be accurately identified by a simple method.