A proxy device has: an address management portion for sending an alternative IP address and an alternative MAC address not used within a network to a server unit when a sleep invocation notification is received from the server unit; a virtual interface creation portion for creating a virtual interface having a server IP address and a server MAC address, which were used by the server unit before the notification is sent; a broadcasting portion for broadcasting a packet indicating that a location of the server IP address and the server MAC address has shifted into the proxy device to the network; a server wakeup processing portion sending a restoration notice to the server unit if the virtual interface receives data destined for the server IP address; and a virtual interface deleting portion for deleting the virtual interface if the server unit indicates restoration from the sleep mode.