In a situation where a host computer or storage system is an initiator and the storage system or another storage system is a target, when the initiator intends to check LUs in the target, if the initiator judges that the number of delay ACKs is set to more than one, it simultaneously issues the same number of check commands—SCSI Inquiry LUN#a and LUN#b—as the number of delayed ACKs, or check commands in multiples of the number of delayed ACK, to the target; and, when receiving check results—SCSI Data-In—in response to the check commands from the target, sends an acknowledgement to the target. Accordingly, when the number of delayed ACKs set in the TCP in the initiator is more than one, the initiator simultaneously issues check commands to the target designating the same number of LUs as the number of delayed ACKs, and the responses will not be influenced by the delayed ACK.