A discharge lamp lighting apparatus includes a DC/DC converter for converting an input direct voltage to a direct voltage of a different voltage value than the input direct voltage by switching and then outputting the converted direct voltage; a discharge lamp driver for converting the output direct voltage, which is supplied from the DC/DC converter, to a voltage suitable for driving a discharge lamp; a pulse width controller for generating a pulse width controlled switching control signal based on a reference pulse and then supplying the switching control signal to the DC/DC converter; and a microprocessor for controlling the apparatus as a whole and supplying to the pulse width controller a pulse width control signal and the reference pulse in synchronism with the pulse width control signal.