A storage switch with bandwidth control function for preventing discarding of packets for bandwidth breach when sending or receiving storage data using an iSCSI protocol on a wide area network having a covenant (guaranteed) bandwidth, when the quantity of storage data traffic sent by the initiator or target was judged a bandwidth breach or violation. The traffic amount is predicted from the Expected Data Transfer Length contained in the read request of the iSCSI command and the Desired Data Transfer Length contained in the R2T command, when that command is sent to the target and the initiator and the bandwidth is regulated by controlling the transmission timing of that command.