PURPOSE: To surely check an extended memory in a short time by giving an access to a memory toward a leading address from the final address for the text of the memory including an extended option memory after obtaining the final address of an extended option memory.

CONSTITUTION: When an MPU 1 runs a check program for the contents of a memory (character pattern) 2, the final address of an extended option memory is obtained in an address operation/generation means (address operation/ generation part) 6 based on the ON/OFF information on the option bit set at an option bit register 3. Then an access is given to the memory 2 toward the leading address from a final address. Thus the normality of the option memory is early confirmed and its countermeasure is quickly applied.