A light source drive device includes a supply unit that supplies a high-frequency first drive signal and a second drive signal whose frequency is lower than a frequency of the first drive signal to a discharge lamp which has a pair of electrodes, and a control unit that controls the supply unit so that the first drive signal and the second drive signal of fixed durations are alternately supplied and that controls the supply unit so that the first drive signal is supplied in a case where a voltage between the pair of electrodes is below a threshold.