The discharge lamp lighting apparatus includes a high-voltage generating coil connected in series to a discharge lamp for applying a high voltage to the discharge lamp to turn on the lamp, an inverter for inverting a dc voltage into an ac voltage in order to supply a lamp current to the discharge lamp on an alternating basis through the high voltage generating coil, a lamp voltage detecting circuit for detecting a voltage across the discharge lamp as a lamp voltage, and a lamp power control circuit for controlling an ac power supplied to the discharge lamp from the inverter on the basis of the lamp voltage detected by the lamp voltage detecting circuit. The lamp voltage detecting circuit detects the lamp voltage by subtracting a voltage in proportion to a sum of voltage drops across devices lying on a current path over which the lamp current flows other than the discharge lamp from a voltage in proportion to the dc voltage.