the data format of the response data to the data for confirming continuity as fig8 shows the response data to the data for confirming continuity comprises an overall data length 601 which indicates the length of the entire response data ns id 602 which is an ip address of the network storage device 3 at the transmission source nh id 603 which is an ip address of the host computer 1 at the transmission destination s id 605 which is an iscsi name of the network storage device 3 at the transmission source iscsi target h id 606 which is an iscsi name of the host computer 1 at the transmission destination iscsi initiator result 607 for specifying the execution result of the command one of 11 normal end 12 authentication error 13 lun error and data length 604 of s id 605 h id 606 and the result 607 in this case the data to be transmitted for confirming continuity which was transmitted from the host computer 1 is a login command so either u201c 11 u201d or u201c 12 u201d is stored in the result 607 of the response data in s 1043 and s 1044 if the response data to the iscsi login command is not received within a predetermined time the cpu 11 judges this as.