An inventive opto-electric hybrid board includes: opto-electric module portions respectively defined on opposite end portions of an elongated insulation layer, and each including a first electric wiring of an electrically conductive pattern and an optical element provided on a front surface of the insulation layer; and an interconnection portion defined on a portion of the insulation layer extending from the opto-electric module portions, and including an optical waveguide optically coupled with the optical elements. A metal reinforcement layer provided on a back surface of the insulation layer as extending over the opto-electric module portions into the interconnection portion. A portion of the metal reinforcement layer present the interconnection portion has a smaller width than the opto-electric module portions, and the smaller width portion has rounded proximal corners.