1. A structured-text cataloging method for a text searching system, in which a set of texts is searched for specific text contents, comprising the following steps: an already-analyzed-text data generating/cataloging step of cataloging, in a text database, already-analyzed-text data obtained from an analysis of a logical structure of a text to be cataloged, said already-analyzed-text data generating/cataloging step being performed for a plurality of texts to be cataloged; and a structure-index creating step of creating a structure index, by sequentially superposing logical structures of said plurality of texts cataloged in said already-analyzed-text data generating/cataloging step; wherein said structure index has a tree-like structure composed of a plurality of metanodes; wherein a context identifier that uniquely identifies one of said metanodes is assigned to each metanode of said structure index; and wherein a group of structure elements having the same position of appearance and the same element type for a plurality of texts are represented by a single metanode.