The entirety or a part of free space of a second storage device included in a host computer is used as a cache memory region (external cache) outside of a storage apparatus. If Input/Output (I/O) in the host computer is Write, a Write request is transmitted from the host computer to a storage apparatus, the storage apparatus writes data associated with the Write request into a main cache that is a cache memory region included in this storage apparatus, and the storage apparatus writes the data in the main cache into a first storage device included in the storage apparatus. The storage apparatus writes the data in the main cache into an external cache included in the host computer. If the I/O in the host computer is Read, the host computer determines whether or not Read data as target data of the Read exists in the external cache. If a result of the determination is positive, the host computer reads the Read data from the external cache.