A driving device for a discharge lamp includes: a discharge-lamp lighting unit that supplies an alternating current to the discharge lamp to thereby supply electric power to between two electrodes of the discharge lamp; an inter-electrode-voltage detecting unit that detects an inter-electrode voltage applied when predetermined electric power is supplied to between the two electrodes; and a power-supply-condition switching unit that switches, on the basis of the detected inter-electrode voltage, the power supply by the discharge-lamp lighting unit with a predetermined hysteresis given to the switching of the power supply conditions, wherein the power supply conditions are switched by changing at least one of a frequency of the alternating current, a duty ratio of the alternating current, a modulation pattern of the frequency, and a modulation pattern of the duty ratio.