A discharge lamp drive device for driving a discharge lamp including a first electrode and a second electrode, include: a power supply unit which supplies alternating power to the discharge lamp by inputting alternating current between the first electrode and the second electrode, wherein the power supply unit includes a power reduction control unit which reduces the alternating power from a first level to a second level lower than the first level, and a duty ratio control unit which steppedly varies duty ratio of the alternating current in a predetermined period at the time of reduction of the alternating power.