Patent ID: 8129927

Claim:
A driving device of an electric discharge lamp comprising: a discharge lamp lighting unit which supplies power to the electric discharge lamp while alternately switching a polarity of voltage applied between two electrodes of the electric discharge lamp to light the electric discharge lamp; and an anode duty ratio modulating unit which sets at least a first retention period and a second retention period for modulating anode duty ratios, each of the retention periods being a period for retaining an anode duty ratio as a ratio of an anode period in which one of the electrodes operates as an anode at a constant value in one cycle of the polarity switching, and the second retention period having an anode duty ratio different from that of the first retention period and being provided after the first retention period, the anode duty ratio modulating unit having a first modulation mode and a second modulation mode for providing a larger change of the anode duty ratio between the first retention period and the second retention period than a change of the anode duty ratio for the first modulation mode.