An I/O device performs data input and data output between the I/O device and first and second computers. An I/O switch relays input and output data between the I/O device and each of the first and second computers. A device emulator emulates the I/O device when a virtual machine running on the first computer and directly accessing the I/O device is migrated from the first computer to the second computer. A connection controller controls switching connection between any one of the first and second computers and any one of the I/O device and the device emulator. The first computer is connected to the I/O device and the second computer is connected to the device emulator until the virtual machine running on the first computer is stopped, and the second computer is connected to the I/O device after the virtual machine running on the first computer is stopped.