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.