Abstract: An interface unit includes an optical interface circuit outputting a transmitting signal for driving an optical driver in response to input data, a serial interface circuit outputting a transmitting signal for driving a serial driver in response to the input data, a terminal for outputting a signal, and a circuit part for selectively outputting the transmitting signal from one of the optical interface circuit and the serial interface circuit via the terminal, so that at least a pulse width of the transmitting signal output via the terminal satisfies a standard established with respect to the optical driver when the output transmitting signal of the optical interface circuit is output via the terminal.