AV signal output device, AV signal input device, and AV signal input/output system

An AV signal input/output system includes an AV signal output device, an AV signal input device, and a cable which connects between the devices. The AV signal output device includes an existing interface, an optical interface, a selection output controller which selects existing interface differential signals or optical output signals, and outputs an AV signal, and an information identification unit which reads out information of the connected destination of a connector through existing interface signal lines. The information identification unit includes an optical information identification unit which identifies optical information. The AV signal input device includes an existing interface, an optical interface, a selection input controller which selects existing interface differential signals or optical input signals, and outputs an AV signal, and information storage which causes a connector to read out information through existing interface signal lines. The information storage includes optical information storage.