PURPOSE: To save a labor for storing in a magnetic tape device by providing a read only storing area with a back up power source in a central controller and storing boot strap program therein.

CONSTITUTION: The IPL of the central controller 1 is activated by the operation of a load command key on a control console included in a man machine interface device 11. This IPL function is realized by the firmware of a microprogram control, the central controller 1 is initialized according to the activating from the control console to load the boot strap program of a ROM 1a to a main storage device 2 and then activate it. The activated boot strap program initializes the main storage device 2, thereafter, commands a magnetic tape controller 5 to load an operation system. The controller 5 loads the program for establishing the system stored in the magnetic tape device 6 according to the load command and informs the completion of this load to the travelling boot strap program in the controller 1 at the time of the completion thereof.