In a library system in which a virtual library apparatus is interposed between a library apparatus and a data processing apparatus, a collecting means collects access states to a logical volume from the data processing apparatus, a database retains the access states, and a restoring means determines a restoration priority of the logical volume on the basis of the access state, reads out the logical volume from a physical volume retaining the logical volume onto a cache according to the restoration priority, thereby restoring the logical volume to be held in the cache. Even immediately after the cache of the virtual library apparatus is replaced with another new cache, it is possible to avoid a case where the response speed to a mount request (processing request) from the data processing apparatus becomes slower than the response speed during the normal operation before replacement of the cache.