This storage apparatus having a plurality of physical devices for balancing and retaining data sent from a host computer and parity of the data for each prescribed unit includes a load ratio calculation unit for calculating a load ratio of the plurality of physical devices, a load ratio determination unit for determining whether the load ratio of the physical devices calculated with the load ratio calculation unit exceeds a prescribed threshold value, a command ratio determination unit for determining whether a command ratio of either a write command or a read command issued from the host computer exceeds a prescribed threshold value when the load ratio determination unit determines that the load ratio of the physical device exceeds a prescribed threshold value, and a change unit for changing the data and the parity among the plurality of physical devices when the command ratio determination unit determines that the command ratio exceeds a prescribed threshold value.