An I/O device to be connected to a network, which is configured to input and/or output data, includes a self-address storing system configured to store the I/O device address, a receiving system configured to receive data whose destination is an address stored in the self-address storing system, the data being transmitted through the network, a displaying system configured to display at least one of a character string and a graphic form, and an informing execution system configured to execute an informing operation with changing a display state of the displaying system, in response to the receiving system receiving data for confirming the location of the I/O device.