A storage apparatus is provided with a storage area for storing data sent from a host computer, and a virtual/logical volume to which a dynamically variable storage area is allocated from within the storage area, the volume being provided to the host computer, and this storage apparatus is configured to include: a pool area generation unit for generating a plurality of pool areas composed from the storage area; a setting unit for setting, for each of the plurality of pool areas generated by the pool area generation unit, an allocation unit size for allocating a storage area from within the storage area provided by the pool area to the virtual/logical volume; a selecting unit for selecting, when data to be stored in the storage area is sent from the host computer, a pool area from among the plurality of pool areas having the allocation unit size set by the setting unit, in accordance with the size of the sent data; and an allocation unit for allocating a storage area from within the storage area provided by the pool area selected by the selecting unit to the virtual/logical volume.