A method for creating an index for searching a structured document having a document data-structure stored, in a computer. The method to be performed in the computer for creating an index includes the steps of: analyzing a structured document to extract a document data-structure in the structured document; 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 each element in the created logical structure index; and extracting elements for creating the index, based on the logical structure index, by comparing the extracted element appearance number and a first predetermined threshold.