Upstream network interfaces (2-1-2-N) and downstream network interfaces (5-1-5-M) have an upstream PCI-PCI bridge function and a downstream PCI-PCI bridge function, respectively. These network interfaces (2-1-2-N, 5-1-5-M) and a network (3) are incorporated in a system as a single multi-root PCI express switch. The network (3) tunnels TLPs (Transaction Layer Packets) between the upstream network interfaces (2-1-2-N) and the downstream network interfaces (5-1-5-M) or between the downstream network interfaces (5-1-5-M). This enables to distribute and connect a plurality of computers and a plurality of I/Os on a large scale without changing software, root complexes, and I/Os.