A first network device determines whether it is available to transmit division data which is transmitted from a first virtual machine execution apparatus to a second network device which is provided at a side of a second virtual machine execution apparatus among a plurality of network devices, and stores the division data in a storing device when determining that it is not available to transmit, and transmit the division data in the storing device to the second network device when determining that it is available to transmit the division data to the second network device.