To shorten the time from power restoration to the resumption of business operation. During a power failure, a memory controller saves configuration information and directory information of a shared memory to a nonvolatile memory, and saves data of a cache memory to the nonvolatile memory. During power restoration from a power failure, the memory controller returns information of the nonvolatile memory to the shared memory so that it can be updated before the lapse of the initialization time, the micro processor executes online processing based on information of the shared memory, and the memory controller 70 controls the storage area of the cache memory so that it will become gradually writable according to the battery capacity of the battery if the battery capacity of the battery is still gradually increasing even after the lapse of the initialization time.