Disclosed is to prevent deterioration in I/O performance of a computer resulted from a use of the same physical disk among different logical volumes. A volume management server 1010 groups together logical volumes which use the same physical disk of a storage device 1020 as a volume group and allocates a storage area on the physical disk to be used on a priority basis by this volume group to the volume group, and thereby a physical arrangement according to a present physical arrangement of the logical volume can be performed when an automatic expansion of the logical volume is performed thereafter so that the I/O performance deterioration of the computer caused by a mutual interference is avoided at the time of access from the computer 1030 to the storage device 1020.