An I/O device sharing system characterized by comprising: an I/O device (50) shared by a plurality of hosts (20-1 to 20-N); a system manager (10) which sets the I/O device (50); a virtual bridge (40) which virtualizes the I/O device (50); and a network (3) which connects the I/O device (50), the system manager (10), the plurality of hosts (20-1 to 20-N) and the virtual bridge (40) to each other, wherein the virtual bridge (40) includes a connection virtualization unit (41) by which it is detected that an address setting of a plurality of virtual functions provided in the I/O device (50) that is set by the system manager (10) is performed, the virtual function is enabled, or both of them are performed and each host is permitted to access each virtual function.