A projected image generating unit generates a projected image of a two-dimensional image that expresses three-dimensional information, based on three-dimensional data stored in an original image storing unit. A position information storage unit records therein three-dimensional position information of a target pixel that has been detected by the projected image generating unit and the coordinates of the target pixel within the projected image, while keeping them in correspondence with each other. A user inputs a position of a specified point within the projected image by using an input unit. By referring to the position information storage unit, a position obtaining unit obtains three-dimensional position information of the specified point. An area extracting unit extracts a three-dimensional image of a target area containing the specified point, based on the three-dimensional position information of the specified point that has been obtained by the position obtaining unit.