PURPOSE: To prevent the destruction of a program in one and same memory area by providing a means detecting an access of an execution form program to an incorrect address as an error even in a loaded memory area.

CONSTITUTION: When an operating system 5 detects a load request of a program, a memory area 7 is decided and a link map 3 is loaded from a file device 1. Then the size of an accessible area 8 of an execution form program 9 is obtained from the information of the link map 3 and when the loading is possible, after the information of the accessible area 8 of the execution form program 9 is stored to an address information management table 6, the execution from program 9 is loaded to the memory area 7 from the file device 1 to start the program 9. The system 5 checks the content of the access area of the program 9 and the table 6 every time itself if activated and stops the execution of the program 9 in detecting any error.