1. An information providing apparatus for providing additional information associated with position information so that the user can understand the relationship between the additional information and the position, the apparatus comprising: real image obtaining means for obtaining a real image; three-dimensional position obtaining means for obtaining the three-dimensional position where the real image is obtained; building data obtaining means for obtaining data of each building included in the real image based on the obtained three-dimensional position; additional information obtaining means for obtaining additional information based on the obtained three-dimensional position; image synthesizing means for synthesizing the additional information and the real image; and display means for displaying the real image together with the additional information by using a predetermined display window.