The present invention decreases the burden of operation required for specifying the continuity status and the cause of failure of a network storage device. A host computer accepts the specification of the device identifier, that is an identifier of the network storage device in the host protocol which positions in a higher hierarchy than the network communication protocol, and a volume identifier, that is an identifier of the volume. Then based on the specified device identifier, the host computer specifies the network identifier, that is an identifier of the network storage device in the network communication protocol. And continuity is confirmed in the network communication protocol in which the specified network identifier is the destination. Also continuity is confirmed in the host protocol in which the device identifier is the destination. And the volume specified by the volume identifier is accessed.