In at least one embodiment of the disclosure, a discharge lamp driving device includes a discharge lamp lighting unit configured to supply power to a discharge lamp while alternately switching a polarity of a voltage applied across two electrodes of the discharge lamp. A controller performs a modulation control of the power in accordance with a power ratio characterized by the power supplied in a polarity switching period. The controller starts the modulation control at a predetermined time after the power supplied to the discharge lamp reaches a predetermined power value.