A sub headlight system for use in a vehicle that leans into turns, the sub headlight system comprising: a sub headlight unit (13L, 13R) comprising a plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) for illuminating, at one side with respect to a width direction of the vehicle, an area ahead and outward of the vehicle with respect to the width direction of the vehicle; a control part that is adapted to change the brightnesses of the plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) in accordance with the lean angle of the vehicle; and a detection part (22, 23) that is adapted to detect a variable available for obtaining the lean angle of the vehicle, wherein the plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is adapted to change the brightness in accordance with a lean angle of the vehicle, when the lean angle of the vehicle reaches a reference value (K1, K2, K3) that is individually set for each of the sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc), said sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is adapted to exhibit a predetermined brightness, wherein, when the lean angle of the vehicle reaches the reference value (K1, K2, K3), the control part is adapted such that it causes the corresponding sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) to exhibit a predetermined brightness, so that when the vehicle is inclined to one side with respect to the width direction of the vehicle so that the lean angle increases, the brightness of the plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) that illuminate this one side is sequentially increased in the order from the sub headlight light source for which a smaller reference value is set to the sub headlight light source for which a greater reference value is set, the plurality of sub headlight light sources being arranged in a manner so as the reference value (K1, K2, K3) set for the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is greater, an outer edge of an illumination range of the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) having a predetermined illuminance is located more outward with respect to the width direction of the vehicle in a plan view, and the sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) being arranged in a manner so that as the reference value (K1, K2, K3) set for the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is greater, a larger angle is formed in a plan view between an optical axis (AL1, AL2, AL3, AR1, AR2, AR3) of the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) and a center line of the vehicle in a front-back direction thereof. a sub headlight unit (13L, 13R) comprising a plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) for illuminating, at one side with respect to a width direction of the vehicle, an area ahead and outward of the vehicle with respect to the width direction of the vehicle; a control part that is adapted to change the brightnesses of the plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) in accordance with the lean angle of the vehicle; and a detection part (22, 23) that is adapted to detect a variable available for obtaining the lean angle of the vehicle, wherein the plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is adapted to change the brightness in accordance with a lean angle of the vehicle, when the lean angle of the vehicle reaches a reference value (K1, K2, K3) that is individually set for each of the sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc), said sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is adapted to exhibit a predetermined brightness, wherein, when the lean angle of the vehicle reaches the reference value (K1, K2, K3), the control part is adapted such that it causes the corresponding sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) to exhibit a predetermined brightness, so that when the vehicle is inclined to one side with respect to the width direction of the vehicle so that the lean angle increases, the brightness of the plurality of sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) that illuminate this one side is sequentially increased in the order from the sub headlight light source for which a smaller reference value is set to the sub headlight light source for which a greater reference value is set, the plurality of sub headlight light sources being arranged in a manner so as the reference value (K1, K2, K3) set for the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is greater, an outer edge of an illumination range of the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) having a predetermined illuminance is located more outward with respect to the width direction of the vehicle in a plan view, and the sub headlight light sources (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) being arranged in a manner so that as the reference value (K1, K2, K3) set for the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) is greater, a larger angle is formed in a plan view between an optical axis (AL1, AL2, AL3, AR1, AR2, AR3) of the sub headlight light source (13La, 13Lb, 13Lc, 13Ra, 13Rb, 13Rc) and a center line of the vehicle in a front-back direction thereof.