PURPOSE: To simply change a program or the number of loading sheets of an external auxiliary memory part by using a loading designation file to instruct the start of the program to be loaded or a system.

CONSTITUTION: A CPU 1 starts a boot loading program stored in a ROM 3 when a power source is turned on or reset. In this case, a floppy disk containing a loading designation file shown in a figure (a) is put into a floppy disk deice 5. A boot loading program is started and reads a loading designation file 12 onto a memory. Then it is decided by data 15 whether a file to be loaded exist or not. If so, the relevant file is loaded. This step is repeated after the floppy disk is exchanged with the one shown in a figure (b). Finally the floppy disk is exchanged with the one shown in a figure (c) and a start instruction is produced. Then a boot loading system is started when coincidence is secured between the designated number of sheets stored in the file 12 and the counted number of sheets.