A memory protection method of dividing the address space of a memory into two or more protection regions, and protecting the memory from an unauthorized access to a protection region by a program includes a definition step of defining the relation between protection regions, a determination step of, when the relation between the protection regions is an inclusion relation, determining that an included protection region cannot directly access an including protection region and the including protection region can directly access the included protection region, and a step of, when an access to the protection region determined to be able to be directly accessed is requested, permitting a direct access to the protection region determined to be able to be directly accessed, and prohibiting a direct access to the protection region determined to be unable to be directly accessed.