To precisely determine abnormality of a feeder or a light source unit in dimming and controlling the light source unit.

A dimming control system 1 includes: the light source units 3-1 to 3-3 respectively having LEDs 13-1 to 13-3; and a control unit 2 connected to the light source units 3-1 to 3-3 respectively through the feeders. The control unit 2 has: switch parts 21-1 to 21-3 respectively series-connected to the light source units 3-1 to 3-3 and to dim and control the LEDs 13-1 to 13-3 by repeatedly switching ON and OFF in a prescribed cycle; electric current detection circuits 8-1 to 8-3 and voltage detection circuits 9-1 to 9-3 to detect an electric current or voltage respectively supplied through each of the feeders; and a CPU 5 to determine that each of the feeders or the light source units 3-1 to 3-3 is abnormal when value of the detected electric current or voltage exceeds a prescribed range when the switch parts 21-1 to 21-3 are ON.