To improve the reliability of data in a cache memory without any deterioration in system performance.

For a disk part 1 which stores data, this disk system is equipped with an MPU 22 which controls data access to the disk part 1 and cache memory parts (23-1) and (23-2) having cache memories wherein data are temporarily held and handles access made by a host computer. A data transfer path (27) is provided which interconnects the cache memory parts (23-1) and (23-2) and data are transferred between the cache memory parts (23-1) and (23-2) through the data transfer path (27).