PURPOSE: To attain transmission of a multi-document to an ISDN network by sending the multi-document unified into one document when a transmission destination of the multi-document is a facsimile network.

CONSTITUTION: When the storage of an original is finished, whether or not an incoming number indicates a destination number of an ISDN facsimile network is discriminated. In the case of a multi-document, a switch used to decide whether or not the multi-document is to be unified into one document is watched. When the switch is set, the multi-document is combined into one document, a counter for a document number is set to 1 and then an original is sent. The multi-document is combined in such a way that a list of a destination table is indexed and a 2nd documents, if so, is combined into a 1st document. Thus, the transmission of the multi-document to the ISDN is attained and 2nd storage of an original is not required.