A storage device is provided with: a first management section that manages a storage area provided by one or more hard disk drives on a basis of a predetermined unit created using one or more parameters; a second management section that manages, on a basis of a pool configured by at least one or more of the units, a management policy about the capacity of the pools and a threshold value of the storage capacity of the pools; a power supply control section that controls each of the hard disk drives of the unit under the management of the first management section to be in either a first turn-ON state or a second turn-ON state with a low power consumption; and a control section that selects, when the storage capacity of any of the pools exceeds the threshold value, the management policy of the pools, and any of the managed parameters considered optimum to serve as the unit of the storage area, and after making the power supply control section to change the state of the hard disk drive of the selected unit from the second turn-ON state to the first turn-ON state, adds the unit of the storage area to the capacity of the pool. With such a configuration, the storage device can achieve reduction of power consumption, simplification of management, and increase of use efficiency of storage resources.