A journal write unit writes journal data into a third storage device. The journal
data includes an identifier of a logical volume in a first storage device into
which data has been written, information of a location in which the data is stored
in the logical volume, update time which is current time acquired from a timing
mechanism, and the data. A second write unit refers to update time of the journal
data stored in the third storage device, selects journal data for which a difference
between current time acquired from the timing mechanism and the update time is
longer than a detection time stored in the third storage device, and writes the
data into a place indicated by the location information, in a logical volume in
the second storage device in the order of update time in the selected journal data.