In a storage system, a real page is allocated from a pool to a write destination virtual page in a virtual volume. The real page includes multiple real regions. The storage system moves all valid data stored in two or more move-source real pages respectively allocated to two or more virtual pages, to move-destination real pages the number of which is less than the number of move-source real pages in units of real regions. Each piece of valid data can be used by any one of the access sources. The storage system writes the predetermined data to all move-source real regions in each of move-source real pages, so that each of the move-source real pages is set as a recovery target real page which is a real page storing only the predetermined data, and performs real capacity recovery for making each recovery target real page into an unallocated state.