A secure storage system for securely accessing a storage device on a network and improving volume management scalability, consisting of a client having a VPN capability; a storage device in an SAN; a management apparatus having a means for managing a storage capacity and a logical volume allocated to the storage device; a converter for converting a protocol used in the SAN to a protocol used in a LAN/MAN/WAN and vice versa; and a conversion apparatus having the VPN capability. A VPN is provided between the client and the conversion apparatus. The conversion apparatus is provided with a mapping between the VPN and an access range of the storage device. A VPN-ID is used for identifying the VPN. An address in the logical volume is used for the access range of the storage device.