A memory system includes a volatile first storing unit, a nonvolatile second storing unit in which a plurality of memory cells that can store multi-value data are arranged, the memory cells having a plurality of pages, and a controller that performs data transfer between a host apparatus and the second storing unit via the first storing unit. The controller includes a save processing unit that backs up, when, before data is written in the second storing unit in a write-once manner, data is written in a lower order page of a memory cell same as that of a page in which the data is written, the data of the lower order page and a broken-information-restoration processing unit that restores, when the data in the lower order page is broken, the broken data using the backed-up data.