To improve throughput in data transfer in a remote I/O system, this invention provides a computer system including: a host computer; a device which communicates with the host computer; and a network which connects the host computer and the device, in which the device is coupled to the network via a device bridge including a bridge memory, and the host computer includes a host memory and a device driver. The device driver writes, when at least one of data and an address is written in the host memory, in the bridge memory the at least one of the data and address stored through the writing in the host memory; and sends a data transfer request to the device bridge, and the device bridge reads, upon reception of the data transfer request, an address from a predetermined area; and reads data from an area that is indicated by the read address.