An encoding circuit encodes a NRZ code into a transmission line code. A decoding circuit decodes the transmission line code into a NRZ code. If an operation-mode specified by a setting signal is a normal-mode, a transmission switching circuit provides transmit-data received from an input terminal to the encoding circuit to output the encoded transmit-data as communication-data from a communication terminal. If the operation-mode is a sleep-mode, the transmission switching circuit outputs the transmit-data received from the input terminal as the communication-data from the communication terminal. If the operation-mode specified by the setting signal is a normal-mode, a reception switching circuit provides the communication-data received from the communication terminal to the decoding circuit to output the decoded communication-data as receive-data from an output terminal. If the operation-mode is a sleep-mode, the reception switching circuit outputs the communication-data received from the communication terminal as the receive-data from the output terminal.