When a host apparatus transfers/swaps stored information between user sectors in a storage device for the purpose of defragmentation or the like, the storage device is allowed to perform the data transfer or swap without transmission between the host apparatus and the storage device after the command is received by the storage device; and consistency in stored information identification is maintained between the host apparatus and the storage device even if the operation is interrupted. In one embodiment, information stored in the destination user sector LBA(Y) is copied to the dummy sector LBA(D), its entry is written in the mapping table RDM, information stored in the source user sector LBA(X) is copied to LBA(Y), and then the RDM entry is erased.