To realize the automatic change of the setting of a composition region so as to perform an attractive composition processing by a method wherein a data processor for perform the composition processing consists of setting means of document composing information, of the information on composition size, of composition data, of composition regulations and the like, a processing work controlling means and the like.

A data processor 1 consists of a display processing means 1A, a processing work controlling means 1B, a document composing information setting means 1C on the constitution of a series of documents and a composition size setting means 1D for setting and holding the maximum size among composition sizes to be able to employ. In addition, the data processor consists of a composition data setting means 1E for setting and holding the composition data of a composition region for starting a composition, a composition regulation setting means 1F for setting and holding the composition regulations of the composition region for starting the composition, a composition arithmetic processing means 1G for arithmetic processing the composition data of the setting means 1E in accordance with the composition regulations held here and a storing means 1H for storing various composition data, the composition regulations, a composition processing result and the like.