A headlight system for use in a vehicle that leans into turns, the headlight system comprising: a main headlight configured to be turned on irrespective of inclination of the vehicle and illuminate an area ahead of the vehicle; a sub headlight including a plurality of light sources (13La-13Lc, 13Ra-13Rc) and a lamp body (22,32) that supports the light sources (13La-13Lc,13Ra-13Rc), the plurality of light sources (13La-13Lc,13Ra-13Rc) being configured to be turned on when the vehicle is inclined; and a control device being configured to, when the vehicle is inclined to the right with respect to a width direction of the vehicle, turn on among the plurality of light sources (13La-13Lc,13Ra-13Rc) a light source that illuminates an area ahead and to the right of the vehicle with respect to the width direction of the vehicle, and when the vehicle is inclined to the left with respect to the width direction of the vehicle, turn on among the plurality of light sources (13La-13Lc,13Ra-13Rc) a light source that illuminates an area ahead and to the left of the vehicle with respect to the width direction of the vehicle, characterized in that the control device is supported on the lamp body (22,32) and includes a single reception port as a receiver that receives data in a format for digital data transmission, the data being used for a control of turning-on of the plurality of light sources (13La-13Lc,13Ra-13Rc) of the sub headlight, wherein the control device is configured to receive digital data from an external device via the single reception port, the external device is different from the control device and mounted in a vehicle part other than the headlight system and configured to receive and process outputs made from a plurality of sensors, to convert the outputs into the format for digital data transmission, and transmit the resultant to the control device. a main headlight configured to be turned on irrespective of inclination of the vehicle and illuminate an area ahead of the vehicle; a sub headlight including a plurality of light sources (13La-13Lc, 13Ra-13Rc) and a lamp body (22,32) that supports the light sources (13La-13Lc,13Ra-13Rc), the plurality of light sources (13La-13Lc,13Ra-13Rc) being configured to be turned on when the vehicle is inclined; and a control device being configured to, when the vehicle is inclined to the right with respect to a width direction of the vehicle, turn on among the plurality of light sources (13La-13Lc,13Ra-13Rc) a light source that illuminates an area ahead and to the right of the vehicle with respect to the width direction of the vehicle, and when the vehicle is inclined to the left with respect to the width direction of the vehicle, turn on among the plurality of light sources (13La-13Lc,13Ra-13Rc) a light source that illuminates an area ahead and to the left of the vehicle with respect to the width direction of the vehicle, characterized in that the control device is supported on the lamp body (22,32) and includes a single reception port as a receiver that receives data in a format for digital data transmission, the data being used for a control of turning-on of the plurality of light sources (13La-13Lc,13Ra-13Rc) of the sub headlight, wherein the control device is configured to receive digital data from an external device via the single reception port, the external device is different from the control device and mounted in a vehicle part other than the headlight system and configured to receive and process outputs made from a plurality of sensors, to convert the outputs into the format for digital data transmission, and transmit the resultant to the control device.