A cable assembly comprising: a flat cable (103, 103A) having a shape in which a length in a width direction is longer than a length in a height direction, the height direction being perpendicular to a direction in which the cable (103, 103A) extends, the width direction being perpendicular to both the height direction and the direction; a connector (101, 102) that is provided at an end of the cable (103, 103A) in the direction in which the cable (103, 103A) extends; a plurality of electric transmission lines (136a, 136b, 136c, 136d, 136e, 136f, 136g) configured to transmit an electric signal; and a plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) configured to transmit an optical signal, wherein the plurality of electric transmission lines (136a, 136b, 136c, 136d, 136e, 136f, 136g) and the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) are provided so as to extend across the cable (103, 103A) and the connector (101, 102), the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) are provided so that the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) are disposed in parallel with one another in the width direction, characterized in that at least one of the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) is provided at each of ends of the cable (103, 103A) and the connector (101, 102) in the width direction, and the plurality of electric transmission lines (136a, 136b, 136c, 136d, 136e, 136f, 136g) are provided inside the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) in the width direction and disposed in parallel with one another in the width direction. a flat cable (103, 103A) having a shape in which a length in a width direction is longer than a length in a height direction, the height direction being perpendicular to a direction in which the cable (103, 103A) extends, the width direction being perpendicular to both the height direction and the direction; a connector (101, 102) that is provided at an end of the cable (103, 103A) in the direction in which the cable (103, 103A) extends; a plurality of electric transmission lines (136a, 136b, 136c, 136d, 136e, 136f, 136g) configured to transmit an electric signal; and a plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) configured to transmit an optical signal, wherein the plurality of electric transmission lines (136a, 136b, 136c, 136d, 136e, 136f, 136g) and the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) are provided so as to extend across the cable (103, 103A) and the connector (101, 102), the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) are provided so that the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) are disposed in parallel with one another in the width direction, characterized in that at least one of the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) is provided at each of ends of the cable (103, 103A) and the connector (101, 102) in the width direction, and the plurality of electric transmission lines (136a, 136b, 136c, 136d, 136e, 136f, 136g) are provided inside the plurality of optical transmission lines (113a, 113b, 113c, 113d, 123a, 123b, 123c, 123d) in the width direction and disposed in parallel with one another in the width direction.