A discharge lamp lighting device can reduce a variation in luminous flux at the time when the polarity of a voltage to be applied to the discharge lamp is inverted, prevent an excessively large amount of current from flowing through the discharge lamp at the time of starting, prevent the fade-out of discharge when the discharge mode returns from an arc discharge mode to a glow discharge mode, and reduce the ripple of a lamp current in a normal lighting mode. A coil is provided in an output current path of a power supply circuit comprising, for example, a step-down chopper, and a smoothing capacitor is provided in the next stage of the coil so that it selectively is turned on or off by a switching element. An inverter comprising, for example, a full bridge is provided in the next stage of the smoothing capacitor.