PURPOSE: To reduce remarkably the fatigue of eyes to television viewing in a dark room by adding a photoelectric means detecting external light.

CONSTITUTION: A CdS cell 9 is a photodetector converting the intensity of light into a resistance value, and when the external light changes lightly, the resistance value of the CdS cell 9 is reduced by the external light. Then the resistor 7 and the CdS cell 9 are connected in parallel, the combined resistance value is decreased, the collector voltage of a transistor 8 is increased and a current flowing to a pin 22 of an integrated circuit 1 connected thereto is increased, the current of a display LED 2 is increased and the lightness is increased. When the external light is dark, the operation above is reversed and the display LED 2 is dark.