A size storage unit stores therein a block size of a memory element. A buffering unit executes buffer processing configured to store data received from a RAID (Redundant Arrays of Inexpensive/Independent Disks) controller into a buffer, and to write the data stored in the buffer into the memory element. A stripe-size receiving unit receives a stripe size that indicates a size of a unit of access at time of access to the memory element by the RAID controller. Writing processing is configured to write data received from the RAID controller into the memory element without executing the buffer processing by the buffering unit, when the stripe size is n times of the block size (n is a positive integer).