PURPOSE: To unify loading methods independently of the kinds and constitution of devices by transferring plural files stored in a floppy disk to plural memory areas at the time of IPL.

CONSTITUTION: The floppy disk 1 stores a main loader 3 and files 4, 5. A main storage device 2 forms a memory space 6. The main loader 3 is the file to be read out from the disk 1 at first when IPL is started and stores various information for loading plural files 4, 5 to respective areas P, Q of the memory space 6. In addition, the main loader 3 stores also address information X1 to be started at its execution after the end of IPL. At the time of IPL, the files 4, 5 are loaded to the different areas P, Q of the memory space 6 and a program is executed from the address X1.