The storage apparatus is provided with a host interface adapter unit, a storage interface adapter unit, a cache memory unit storing data temporarily, a switch unit connecting the host interface adapter unit, the storage interface adapter unit, and the cache memory unit, a compressed data circuit unit producing compressed data based upon writing data into the physical storing device, and a compressed data saving unit saving compressed data produced in the compressed data circuit unit, where the compressed data circuit unit compressed reading data at a reading time of the data from the physical storing device, and compares the compressed data with compressed data corresponding to reading data saved in the compressed data saving unit with each other, and detects data rigging.