A printer-side controller of a printer repeats transmission of connection confirmation data while response data is received in response to the connection confirmation data. A device-side controller of the connectable device forward the connection confirmation data which is received after transmission of the response data to another connectable device connected thereto. Further, when the printer-side controller confirms connection with any of the plurality of connectable devices by receiving the response data, the device-side controller of the connectable device for which the connection is confirmed stores in the device-side identifier storage memory the identifier corresponding to the position of the connectable device, which is stored in the printer-side identifier storage memory of the printer.