1. A position and orientation measuring apparatus comprising: a storage unit constructed to store character region specifying information and position information in association with a character region placed in a physical space; a character region detection unit constructed to detect a character region from first captured image data obtained by capturing an image of the physical space by an image sensing apparatus, using the character region specifying information stored in the storage unit; an image position information detection unit constructed to detect image position information of an index corresponding to the detected character region; and an estimation unit constructed to estimate a position and orientation of the image sensing apparatus upon capturing the captured image data based on image position information of the detected character region, in the first captured image data, and the position information which is stored in the storage unit and corresponds to the detected character region, wherein the character region detection unit comprises: a contour extraction unit constructed to extract contours in the captured image data; a setting unit constructed to set a character region candidate using the contours; a normalization processing unit constructed to normalize a size of the character region candidate; and a character recognition processing unit constructed to apply character recognition processing to the normalized character region candidate.