N_Port_Name information capable of distinctly identifying a host computer has seen set in a microprocessor 42 of a storage controller 40 prior to start-up of host computers 10, 20, 30; upon startup of the host computers 10, 20, 30, when the storage controller 40 receives a frame issued, then the microprocessor 42 operates to perform comparison for determining whether the N_Port_Name information stored in the frame has been already set in the microprocessor 42 and registered to the N_Port_Name list within a control table maintained. When such comparison results in match, then continue execution of processing based on the frame instruction; if comparison results in failure of match, then reject any request.