The present invention relates to a discharge lamp lighting apparatus which can prevent an increase of loss and a rise of temperature in the area where discharge lamp tube voltage is low. The power conversion circuit 1 converts the input power Pin to output the DC power Pd. The discharge lamp driving circuit 5 converts the DC power Pd supplied from the power conversion circuit 1 to output AC voltage Vo and AC current Io. The controller 2 provides constant power control for maintaining the AC power Po provided by the AC voltage Vo and AC current Io to be constant when the AC voltage Vo is higher than the predetermined value V1, and provides power reduction control for reducing AC power Po to the power conversion circuit 1 when the AC voltage Vo is lower than the predetermined value V1.