1. A document structure inspection method comprising the steps of: conducting a first inspection on an individual element name basis to determine whether a structured document is consistent with a corresponding first document structure definition written in a document structure definition language; in the case that an inconsistency occurs during the first inspection, suspending the first inspection and searching a document structure alteration rule library that is a collection of a plurality of document structure alteration rules for an applicable document structure alteration rule based on an inconsistent element name that appears in the structured document; wherein said document structure alteration rule sets a type indicating “add” or “replace,” an applied definition, an operation element and a relevant document structure definition of a second document structure definition, the type indicating “add” designates an element to be added in the second document structure definition and the type indicating “replace” designates an element to be replaced in the second document structure definition corresponding to the inconsistent element name; conducting a second inspection on an individual element name basis by use of the second document structure definition corresponding to the inconsistent element name in the document structure alteration rule found through the search; and when the second inspection has reached the end of the second document structure definition, resuming the first inspection from the inconsistent element of the first document structure definition if the type of the used second document structure definition is “add” or from an inspection position next to the inconsistent element of the first document structure definition if the type of the used second document structure definition is “replace”.