PURPOSE: To realize a model with different system specification with the aid of the same hardware by writing contents of an illegal instruction code checking table complying with the system specification from a system control processor when a system is initialized.

CONSTITUTION: When the system is initialized, the system control processor 3 decides under what kind of the system specifications a basic processor 2 operates, selects one out of models A, B and C according to the decision, reads out the contents of the selected model, and writes them in the illegal instruction code checking table 7 through a processor bus 4 and a processor interface 9. For the sake of writing, the checking table 7 is configured with RAMs.