To perform failure-free high quality communication in terms of security on a network even if document data in a different format is attached to a document by adding information showing an access program that can process the document data to document data and transmitting it.

A system bus 101 mutually connects various components of a document processor for data transmission and reception. A CPU 102 performs transmission and reception processings of document data. A ROM 103 stores a fixed program that is necessary to start an OS to control the document processor and to access the various components. When document data of a format that is different from the data current format is attached to one piece of document data in such a configuration, contracted image data corresponding to the document data is produced. And the contracted image data and information showing an access program that can process document data are added to the document data and are transmitted.