Data in a storage area to be returned from among storage areas of a storage system is deleted without fail, thereby ensuring data security.When a user's storage-on-demand management program 24 is activated in response to a return request from user A's console terminal 18, the return request is transferred via a communication network 14 to a server 16, and a provider's storage on-demand management program 30 makes a request to a storage management program 32 for volume initialization and data deletion. After the storage management program 32 issues a volume initialization command after receiving the above request, a control program 76 is activated to initialize the designated volume. Subsequently, the user A's volume access right is deleted by the processing executed by the provider's storage-on-demand management program 30, and it is reported to the console terminal 18 that the volume initialization and the volume separation have been conducted.