PURPOSE: To provide a light control device of motor-driven vehicle which controls the illuminance of lamps according to the traveling circumstances, and reduces the consumption of the power of a battery.

CONSTITUTION: In a motor-driven vehicle 11 provided with a means 47 to sense the opening of a means to change the vehicle speed, a means 48 to sense vehicle speed, a means 49 to process the sensed data, and a means 44 to drop and stabilize the output voltage of a battery 32, a means 45 to change the output voltage of the battery 32 where lamps 19, 28, 51 are connected is provided to control the illuminance of the lamps 19, 28, 51 according to the opening of the means to change the vehicle speed and the change of the vehicle speed.