There is provided a technique of accessing a memory of a processor from a peripheral device, thereby the security is ensured while efficiency is being pursued. An address converter 14 includes an address conversion table for converting an effective address into a physical address. The address conversion table stores the effective address to which an area in a memory of a processor unit 10 is allocated to each peripheral device 30 and identification information of an access source to which access permission is given, in association with each other. When the peripheral device 30 accesses, the address converter 14 determines to permit access to the effective address under the condition that the device identification information, included in an access request packet, by which the peripheral device 30 can be uniquely identified, matches the identification information of the access source corresponding to the effective address, in the address conversion table, designated by the access request packet.