Controller for controlling nonvolatile memory unit

A controller writes, after writing data into a nonvolatile memory unit, new management information that reflects the data wiring, into an area of the memory unit other than an area of the nonvolatile memory unit, which stores last management information. After that, the controller writes an old management information flag in relation to the last management information. Further, the controller searches the memory unit for updated, normal management information when initializing the memory system. If it does not find updated, normal management information, the controller restores updated management information on the basis of normal old management information related to the old management information flag.