When an H signal of H/L binary signals is input into a control signal input terminal, a PWM signal is output from a multivibrator. When this PWM signal is input into a power supply circuit via a voltage converter circuit, such a control is repeated that a rated current flows through an LED at an ON time of the PWM signal and a supply of current to the LED is stopped at an OFF time of the PWM signal. An average current flowing through the LED is lowered and thus an emission of light is weakened, nevertheless an emitted light of the LED can be kept white because the rated current is supplied to the LED while the LED emits the light.