1. A method for creating an index for searching a structured document having a document data-structure stored, the method comprising the steps, to be performed by the computer, of: analyzing the structured document to extract the document data-structure; normalizing the extracted document data-structure to create a logical structure index composed of a plurality of elements having a hierarchical structure; extracting an appearance number of a terminal element positioned at an end in the created logical structure index; obtaining an element for creating an index for packaging a plurality of the terminal elements which have been counted among the extracted appearance number, having same element names, and are present in different hierarchical positions of the logical structure index, when comparing the extracted appearance number to a first predetermined threshold indicates that the extracted appearance number is larger than the first predetermined threshold; and creating a packaged index from a path of the obtained element in the logical structure index.