PURPOSE: To reduce the time of awaiting the processing result by a host and to improve the efficiency of an electronic mail service by identifying the transmission of a control document and a normal document and executing the former transmission with priority.

CONSTITUTION: When a control document(CD) transmission request is sent, it is outputted to a CD edit task 36 via an operation task 33. Then the CD is edited in the task 36 and the result is written in a disk device 4, and after confirming its completion reply to be returned to the task 33 via the task 36, a queue is set to the last of an 8 call queue 32 for priority transmission reservation, the transmission processing is sequentially implemented, and when the queue of the reservation queue 32 is finished, a normal communication reservation (8 calling queue) 31 is processed. The processing is all finished and a document file is deleted from the device 4. That is, since the transmission of the CD is processed with priority, the extraction of the normal document is implemented quickly and the wait time is reduced.