To cancel performance difference due to the extended memory mounting of each PC(personal computer device), and to escape the waste of a resource such as the preparation of an exclusive extended memory for each PC.

PC 2.1-2.n are provided with an outside shared memory device 1. At the time of setting the environment of the shared memory device 1, each valid memory capacity is set for each PC 2.1-2.n. The initial address of each valid memory capacity is calculated based on this valid memory capacity and the number of the connected PC, and this is communicated to each PC 2.1-2.n. Each PC receives this communication, calculates an extended memory capacity and a memory map, and communicates it to a CPU. Afterwards, each PC 2.1-2.n can use the shared memory device 1 as the extended memory.