There are provided a memory space allocation method and a memory space allocation device that aim at higher-speed accesses when a memory is shared by a plurality of circuits. In this memory, one data is accessed by issuing addresses a plurality of times. Memory allocation is performed so that high-order addresses of memory spaces of an external memory 505 may be maximally shared by a plurality of circuits 501. When the high-order addresses are common, a memory control circuit does not transfer the high-order addresses, thereby reducing the number of transfers of the high-order addresses. Therefore, the higher-speed access is achieved.