below in detail with reference to the drawings fig2 shows a configuration of a driving circuit according to a first embodiment of the present invention the driving circuit is comprised of a light emitting element 21 a resistor r 21 connected to an anode terminal of the light emitting element 21 a dc dc converter 22 connecting the resistor r 21 and a power supply vcc and a coupling capacitor c 21 the light emitting elements include but are not limited to light emitting diodes and laser diodes the dc dc converter 22 is a boosting circuit which increases the power supply voltage vcc and which supplies the increased power supply voltage vcc to the resistor r 21 and the light emitting element 21 a bias current through the light emitting element 21 is determined by the increased voltage a forward voltage at the light emitting element 21 and resistance of the resistor r 21 an inputted data signal is supplied to the light emitting element 21 via the coupling capacitor c 21 as a modulation signal to provide a voltage swing to the element 21 fig3 shows a circuit configuration of the dc dc converter in the dc dc converter 22 a pulse width modulation pwm control circuit 31 performs such control as turns on and off a transistor 32 to the dc power supply.