PURPOSE: To facilitate a file back-up job by designating the storing places divided in response to the types of terminal processors extended by a back-up processor.

CONSTITUTION: When an extended terminal processor 16, for example, is backed up, a back-up processor 17 designates a storing place in accordance with the type of the processor 16. At the same time, the processor 17 prepares a back-up control program and four tables to designate a proper data record, i.e., the back-up storing place of the processor 16 and stores a back-up file in said storing place. Thus it is possible to omit the manual complicated jobs including the address calculation, etc., and to facilitate a file back-up job.