Abstract: A serial interface apparatus includes a first signal terminal sharing a data transmitting terminal and a second control signal terminal, a second signal terminal sharing a data receiving terminal and a first control signal terminal, and first to fourth buffer amplifiers. Upon receiving two types of second control signals different from each other from the other side apparatuses after transmitting the first control signal to the other side apparatus, the controller executes half-duplex data communication using the two signal terminals by transmitting the serial data signal to the other side apparatus via the first signal terminal, transmitting to the first signal terminal a serial data signal indicating a notice of termination upon end of the serial data signal to be transmitted, and judging as a data communication termination upon reception of the second control signal from the other side apparatus in response to the transmission of the serial data signal.