A management server includes the user management segment information having stored therein a volume managed by a user, a receiving unit for receiving a volume allocation request from a management computer, a sending unit for sending the volume allocation request to a storage system and an updating unit for updating the user management segment information based on the information on the allocated volume received from the storage system. The storage system includes a unit for receiving the volume allocation request from the management server, and based on the volume allocation request, allocating the volume from the unallocated volume that can be allocated by all the users.