An on-vehicle light distribution control system (100) for controlling light distribution of headlights (3), includes a vehicle detecting unit (10) configured to detect a front vehicle (LV) travelling in front of a self-vehicle; a detection difficulty determining unit (12) configured to determine difficulty of the detection by the vehicle detecting unit (10); an operational condition changing unit (14) configured to change an operational condition of light distribution control according to a determination result of the detection difficulty determining unit (12); and a light distribution control state display unit (13) configured to display a present state of the light distribution control for which the operational condition is changed by the operational condition changing unit (14).