PURPOSE: To easily turn on and off a light emitting element and to control its brightness by applying the light emitting element with an AC voltage under waveform control.

CONSTITUTION: A DC stabilized power source 12 and an AC power source 4 are connected to the input of a waveform control circuit 3 and the display device 2 is connected to the output of the waveform control circuit 3. In this case, a control signal from a computer is inputted so as to turn on and off a switching element connected to the AC power source 4, and consequently a voltage is applied to respective light emission devices of the display device 2 connected optionally to the output of the waveform control circuit 3 to turn on the devices. Further, when the brightness is varied, a delay time is provided to the timing of the control signal from the computer and the timing is moved optionally in a half cycle of an AC voltage waveform to control the voltage waveform, thereby varying the brightness. Thus, the light emitting elements are easily turned on and off and the brightness can be controlled.