Structured documents written in a document structure definition language may be inconsistent with a predetermined document structure definition when they are encrypted partly or electronically signed. The document structure inspection method according to the present invention applies a document structure alteration rule to a document structure definition expressing the structure of such structured documents and effects conversion to generate a second document structure definition. The second document structure definition is then checked to determine whether it is consistent with a corresponding, predetermined document structure definition. The document structure alteration rule includes, for instance, a replacement rule for replacing an element contained in a document structure definition by another element, and an addition rule for adding an element to a location after the target document structure definition element.