A lamp drive device L is provided that can both light a lamp and sustain a discharge by applying a trigger voltage while a direct current voltage is supplied from a power supply circuit to the electrodes of lamp before the start of discharge. The device includes a reference amount-of-change storage unit for storing a threshold value T for the amount of change in the electrode voltage before and after start of discharge, a difference calculation unit for calculating the difference (A−B) between the voltage monitor value B after the start of discharge and the voltage monitor value A before the start of discharge, and a lighting status determination unit for determining the lighting status by comparing the difference (A−B) and the threshold value T and making the determination based on the change in voltage before and after the discharge.