The An opto-electro hybrid harness includes, at locations away from first and second connectors, a first relay segment having an EO conversion device, and a second relay segment having an OE conversion device. First and second electric cables lie between the first connector and the first relay segment and between the second connector and the second relay segment. An opto-electric hybrid cable segment lies between the first and second relay segments. An optical fiber is connected at one end to the E0 conversion device and at the other end to the OE conversion device. A first electronic wire of the first electric cable is connected at one end to the first connector and at the other end to the E0 conversion device. A second electronic wire of the second electric cable is connected at one end to the OE conversion device and at the other end to the second connector.