A discharge lamp lighting apparatus adapted to light up a discharge lamp (La), comprising: a d.c. power source section adapted to rectify and smooth an a.c. voltage and to output a d.c. voltage; a step-down chopper circuit connected with an output terminal of the d.c. power source section and adapted to provide power control of a discharge lamp (La); a discharge lamp current detecting circuit adapted to detect a current flowing through the discharge lamp (La) and to provide a discharge lamp current detect voltage; a voltage detecting circuit adapted to detect a voltage (Vla) applied upon said discharge lamp (La); a control circuit block adapted to control an output voltage provided to said discharge lamp (La), wherein said control circuit block comprises: a microcomputer comprising: an A/D converter adapted to convert the voltage (Vla) detected by said voltage detecting circuit into a digital value, and a controller adapted to refer the digital value to a data table, so as to read a power control signal corresponding to the digital value and to output this signal as a PWM signal; said control circuit block further comprising a PWM control circuit adapted to control a switching element of said step-down chopper circuit, and a CR integrating circuit comprising a resistor and a capacitor, the CR integrating circuit being adapted to average out the PWM signal so as to generate a reference voltage; characterized in that the discharge lamp lighting apparatus further comprises a power source ripple detecting circuit adapted to detect a ripple component on said d.c. power source section and to superimpose said detected ripple component to the discharge lamp current detect voltage provided by the discharge lamp current detecting circuit, so as to provide a current detect voltage; wherein said PWM control circuit is adapted to receive the reference voltage and the current detect voltage, to compare the reference voltage and the current detect voltage and to provide a control signal to the step-down chopper circuit to control the switching element based on said comparison, so that a current flowing through said discharge lamp (I La) becomes a constant current. a d.c. power source section adapted to rectify and smooth an a.c. voltage and to output a d.c. voltage; a step-down chopper circuit connected with an output terminal of the d.c. power source section and adapted to provide power control of a discharge lamp (La); a discharge lamp current detecting circuit adapted to detect a current flowing through the discharge lamp (La) and to provide a discharge lamp current detect voltage; a voltage detecting circuit adapted to detect a voltage (Vla) applied upon said discharge lamp (La); a control circuit block adapted to control an output voltage provided to said discharge lamp (La), wherein said control circuit block comprises: a microcomputer comprising: an A/D converter adapted to convert the voltage (Vla) detected by said voltage detecting circuit into a digital value, and a controller adapted to refer the digital value to a data table, so as to read a power control signal corresponding to the digital value and to output this signal as a PWM signal; a microcomputer comprising: an A/D converter adapted to convert the voltage (Vla) detected by said voltage detecting circuit into a digital value, and a controller adapted to refer the digital value to a data table, so as to read a power control signal corresponding to the digital value and to output this signal as a PWM signal; said control circuit block further comprising a PWM control circuit adapted to control a switching element of said step-down chopper circuit, and a CR integrating circuit comprising a resistor and a capacitor, the CR integrating circuit being adapted to average out the PWM signal so as to generate a reference voltage; the discharge lamp lighting apparatus further comprises a power source ripple detecting circuit adapted to detect a ripple component on said d.c. power source section and to superimpose said detected ripple component to the discharge lamp current detect voltage provided by the discharge lamp current detecting circuit, so as to provide a current detect voltage; wherein said PWM control circuit is adapted to receive the reference voltage and the current detect voltage, to compare the reference voltage and the current detect voltage and to provide a control signal to the step-down chopper circuit to control the switching element based on said comparison, so that a current flowing through said discharge lamp (I La) becomes a constant current.