PURPOSE: To inhibit the use of an illegal program by surely checking the legality of a program stored in a machine.

CONSTITUTION: Data for check based on the regular program are previously stored, when starting a program, the data for check are extracted from the program mounted at that time point, the legality of the program mounted at that time point is checked based on the previously stored data for check and these extracted data for check and only when the legality of the program is judged, that program is started.