This invention realizes separate control for each memory area. A memory unit is structured by including a semiconductor memory device capable of memorizing information, the aforementioned memory device is divided into plural memory areas logically and also management table, which is capable of controlling separately each aforementioned memory area for accessing from the outside, is tabled, control information, which prohibits accessing the prescribed memory area of the aforementioned plural memory areas, is provided in the aforementioned management information, and it is prohibited to access the specified memory area from the outside in accordance with control information.