Conventional HDMI optical cables are structured to be unable to normally transmit connection detection between HDMI transmission device and reception device, and unable to avoid a communication failure. Therefore, a phenomenon in which an image is distorted or does not appear occurs. By using an HDMI optical cable and anHDMI optical conversion device in which an electronic circuit switch having a device connection detection function, a voltage converter, a detection sensor, and a detection signal transmission-only wire are embedded in a connector and a cable, respectively, it becomes possible to stably perform connection detection and communication between HDMI transmission device and reception device, and show an image.