A generation-code storage unit stores therein a generation code in association with identification information for identifying the block datum. A generation-code managing unit assigns a new generation code to a detected consecutive data set and any block datum included in writing data other than the consecutive data set and stores the assigned generation code in the generation-code storage unit. A data writing unit adds the new generation code to the block datum or consecutive data set included in the writing data and writes it to a storage unit. A determining unit determines whether the generation code added to a read block datum or consecutive data set is accordant with the generation code of the read block datum or consecutive data set stored in the generation-code storage unit. A data transmitting unit transmits, when the generation codes are accordant, the read block datum or consecutive data set.