In order to solve problems that, when the use area used by data of a certain kind reaches the upper limit value, the cache memory cannot be used even though a space area exists in the use area used by data of other kind and utilization efficiency of the cache memory decreases, and that, when the upper limit value of the use area is discarded, on the other hand, data inside the area held is replaced by other data and disappears, a storage area of a size of a minimum guarantee value corresponding to each computer is set inside a disk cache memory in a control device of a storage device connected to a plurality of computers and a storage area is allocated to each computer in accordance with priority corresponding to each computer.