PURPOSE: To obtain I/O extension of a writer which can process an output device unconsciously by storing DD statement information, which has an identifier on data outputted to a special device, in a spool and by providing a means which identifies allotment and an editing means.

CONSTITUTION: A spool 1 stores DD statement information and data, and the DD statement for a special device [e.g., a magnetic device 4-1 which consists of devices such as a magnetic tape device which is not applied to this system and a direct access memory unit (DASD)] has identifiers. Output data of the spool 1 are inputted to a writer 2 and an allotment part 21 receives these data. The allotment part 21 allots outputting devices in a wide range and outputs the allotment results to a device identification part 22. The identification part 22 sends out signals to an output device 3, if output devices are allotted, and causes an editing part 24 to operate, if special devices are allotted. The DD statement with identifiers for the special device is inputted to the editing part 24. The editing part 24 edits the DD statement for the special device, outputs it and causes the magnetic device 4-1 to operate.