Without using a script that describes a procedure, document parts are extracted from structured documents and inserted or substituted in a template to synthesize a document. An extraction instruction to retrieve document parts, and repetitive duplication and insertion/substitution instructions are provided to the structured documents. Therefore, document part retrieval, repetitive duplication, and a document part (location) in which a document part is to be inserted or substituted are specified, and instructions retrieved from plural inputted structured documents are dynamically synthesized to create a document processing description, so that a document processing description script becomes unnecessary. Consequently, the inconvenience of managing scripts in addition to original documents is eliminated.