Abstract: With this storage apparatus and its control method for presenting multiple virtual volumes to a host apparatus and dynamically allocating to each of the multiple virtual volumes a physical storage area for storing data according to the usage status of each of the multiple virtual volumes, the importance set to each of the multiple virtual volumes is managed, and a storage area is dynamically allocated to each of the multiple virtual volumes. Here, upon dynamically allocating the storage area to each of the multiple virtual volumes, a storage area provided by a plurality of memory apparatus groups respectively configured from a plurality of memory apparatuses is allocated to one or more virtual volumes with low importance among the multiple virtual volumes, and a storage area provided by one of the memory apparatus groups is allocated to other virtual volumes among the multiple virtual volumes.