A storage device according to the present invention has a first volume for storing discontinuous data transmitted from a host computer and a second volume for storing continuous data produced by address-converting discontinuous data, and includes: a data storing unit for converting the discontinuous data transmitted from the host computer into the continuous data and storing the continuous data in one of a plurality of third volumes formed by dividing up the second volume; a data management unit for managing transfer target data that has to be transferred from the third to the first volume, from among the discontinuous data stored in the third volume by the data storing unit; and a volume clearance unit for clearing the third volume having the smallest amount of transfer target data managed by the data management unit by transferring the transfer target data in the relevant third volume to the first volume.