The invention provides a discharge lamp lighting circuit for a discharge lamp which reduces the possibility that the lamp may go out at the time of polarity switching. In the discharge lamp lighting circuit (100), a drive voltage generating unit (12) supplies the AC drive voltage (VL) to a discharge lamp (4) to be driven. A control unit (10) performs a control such that the driving power suppliedto the discharge lamp (4) by the drive voltage generating unit (12) is raised to a level higher than a prescribed target power until a prescribed after-switching assistant period elapses after the drive voltage generating unit (12) is set to switch the polarity of the drive voltage (VL), The control unit (10) sets the length of the after-switching assistant period in such a manner that the greater the lamp current (IL) before the drive voltage generating unit (12) is set to switch the polarity of the drive voltage (VL) is, the shorter the length of the after-switching assistant period is set.