To provide a gateway device which can lower the cost of revising the OS a host computer and can realize a high-speed repeating process.

In the gateway device 20 which repeated a communication between the host computer 1 equipped with a SCSI-2 bus 10 and a control equipment which makes a communication according to the protocol of a control network, an emulating means 21 emulates a SCSI disk and a protocol converting means 22 which receives and processes commands supplied from the host computer 1 through the SCSI-2 bus 10 performed protocol conversion between the SCSI-2 bus 10 and control network. The protocol converting means 22 communicates with the host computer 1 according to the Fast SCSI and Wide SCSI protocols, take a communication frame out of the data started of write command sent from the host computer 1 and sends the taken-out communication frame to the control network, and sends a communication frame received from the control network 3 the the SCSI-2 bus 10 in the data part of read command sent form the host computer.