Virtual Functions (VFs) 602-1 to 602-N of an I/O device are separately allocated to a plurality of computers 1-1 to 1-N. In an address swap table 506, a root domain that is an address space of the computer 1 and mapping information of an I/O domain that is an address space unique to the I/O device 6 are registered. Mapping is set with the VFs 602-1 to 602-N as units. When accessing the VFs 602-1 to 602-N of the I/O device 6 to which each of the computers 1-1 to 1-N is allocated, an I/O packet transfer unit 701 checks the address swap table 506 to swap source/destination addresses recorded in packet headers.