PURPOSE: To control the change of a program easily by storing a constitutional matter analyzing program of a peripheral device in an external storage device of a CPU and executing and analyzing said program to load a peripheral device controlling program.

CONSTITUTION: When the peripheral device 1 requests a CPU2 for loading of a constitutional matter analyzing program PRG4, the CPU2 reads out the PRG4 prepared in the external storage device 8' and transfers the PRG4 to the device 1. The device 1 analyzes the constitutional matter of the device 1 on the basis of the PRG4, forms a constitutional table 6 on the basis of the analyzed result and stores the table 6 in a memory 5. When the device 1 interrupts the CPU2 and transfers the table 6 to the CPU2, the CPU2 transfers the table 6 to a generator GN7 through a transfer control part 19. While referring the table 6, the GN7 forms or selects a controlling PRG9 and stores the PRG9 in the external storage device 8. When a control part 19 transfers the PRG9 to the device 1 by a write command, the device 1 loads the PRG9 to the memory 5 through a loading control circuit 14.