Abstract: When a write access is received from an upper apparatus, a cache control unit develops write data into a data buffer area in a memory, notifies the upper apparatus of a normal end, and thereafter, writes the write data developed into the data buffer area onto a storing medium. An access kind discriminating unit analyzes whether the write access from the host is a sequential access or a random access. A buffer construction control unit selects a data buffer construction of the optimum number of sections in accordance with an access kind and executes the caching operation.