An object of the present invention is to allocate a volume to an appropriate tier in a pool in accordance with the performance of the volume. Multiple tiers 1K are created in a pool 1B. A pool volume that matches the performance required by a tier is allocated to each tier. An information acquisition part 1D acquires information related to respective storage apparatuses 1, 2, and information related to the performance of each volume. A tier control part 1E allocates a pool volume to any tier of the respective tiers, based on the performance information.