An on-vehicle light distribution control system for controlling light distribution of headlights , the on-vehicle light distribution control system comprising: a vehicle detecting unit configured to detect a front vehicle travelling in front of a self-vehicle using an image output by an image sensor that takes images of an area in front of the self-vehicle; a detection difficulty determining unit configured to determine a difficulty of the detection of the front vehicle by the vehicle detecting unit , wherein the detection difficulty determining unit determines that the detection by the vehicle detecting unit is difficult when a number of high brightness pixel groups included in a predetermined area of the image acquired by the image sensor is greater than or equal to a predetermined value; an operational condition changing unit configured to change an operational condition of light distribution control according to a determination result of the detection difficulty determining unit ; and a light distribution control state display unit configured to display a present state of the light distribution control for which the operational condition is changed by the operational condition changing unit , characterized in that the operational condition changing unit reduces a light distribution control upper limit distance as the difficulty of the detection of a front vehicle increases, and increases the light distribution control upper limit distance as the difficulty of the detection of a front vehicle decreases, and in that , to display the present state of the light distribution control, the light distribution control state display unit displays indicators, expressing the present state of light distribution control, on a display device . a vehicle detecting unit configured to detect a front vehicle travelling in front of a self-vehicle using an image output by an image sensor that takes images of an area in front of the self-vehicle; a detection difficulty determining unit configured to determine a difficulty of the detection of the front vehicle by the vehicle detecting unit , wherein the detection difficulty determining unit determines that the detection by the vehicle detecting unit is difficult when a number of high brightness pixel groups included in a predetermined area of the image acquired by the image sensor is greater than or equal to a predetermined value; an operational condition changing unit configured to change an operational condition of light distribution control according to a determination result of the detection difficulty determining unit ; and a light distribution control state display unit configured to display a present state of the light distribution control for which the operational condition is changed by the operational condition changing unit , characterized in that the operational condition changing unit reduces a light distribution control upper limit distance as the difficulty of the detection of a front vehicle increases, and increases the light distribution control upper limit distance as the difficulty of the detection of a front vehicle decreases, and in that , to display the present state of the light distribution control, the light distribution control state display unit displays indicators, expressing the present state of light distribution control, on a display device . <EOS>