By referring to data stored in a capacity management information storage unit, a capacity distribution control unit distributes additional capacity to a supervision target resource whose current available capacity has become less than a prescribed threshold value by using real volumes in the unit's own site when the real volumes in the unit's own site can deal with the situation, and access another site (remote site 50) by using an iSCSI protocol, temporarily use real volume in said another site, and distributes additional capacity to the supervision target resource when the situation can not be dealt with by the real volumes in the unit's own site, and further, an aggregation unit can aggregate data stored in the temporarily used real volumes in said another site to an available region in the unit's own site, and release the temporarily used real volumes in said another site.