An allocation request for requesting allocation of a target virtual area with respect to target data issued to a system program includes a target ID corresponding to the target data. In response to the allocation request, whether or not the target ID is included in data map information is determined. When it is included in the data map information, the system program determines whether or not a target physical area is included in a storage apparatus. When the target physical area is included in the storage apparatus, the system program reserves a free area in a non-volatile memory as a target memory area, copies target data stored in the storage apparatus to the target memory area, changes the target physical area in the data map information to the target memory area, and writes an association between the target virtual area and the target memory area into the volatile memory.