The storage control device of this invention allocates the physical storage area in RAID groups to virtual volumes in units of chunks including multiple pages.To the virtual volume 5, in accordance with write accesses from the host 20, the physical storage area in the pool is allocated. A RAID group 6 in the pool includes multiple chunks 7. Each chunk 7 includes multiple pages 8. To the virtual volume 5, the physical storage area is allocated in units of chunks 7. From the allocated chunks 7, the pages 8 required for writing write data are used.