Abstract: Provided is an optical interface which can continuously perform data transmission even in the case where an optical fiber cable breaks down, and can achieve a highly reliable transmission system. The optical interface is for converting full duplex high-speed serial electric signals and the like complied with an IEEE1394.b to optical signals. The optical interface comprises: a double transmission line made up of a main transmission line and a spare transmission line; an malfunction detection unit for detecting a transmission malfunction occurring in the main transmission line; and a switching unit for switching the transmission line from the main transmission line to the spare transmission line when the malfunction detection unit detects a transmission malfunction in the main transmission line.