A memory system including a nonvolatile semiconductor storage device includes: a nonvolatile memory unit that includes a first data area in which data is frequently rewritten and a second data area in which data is hardly rewritten; and a control unit. The control unit sequentially selects logical block addresses in the second data area in which data is hardly rewritten and updates physical block addresses at new rewriting destinations in the first data area in which data is frequently rewritten to physical block addresses corresponding to the logical block addresses selected.