To provide a discharge lamp lighting device in which a sufficient service-life of a discharge lamp is obtained even if a hot-cathode type discharge lamp is PWM dimmed and it is not necessary to increase electric power involved in auxiliary heating.

The discharge lamp lighting device includes a discharge lamp lighting circuit OC to light the hot-cathode type discharge lamp DL having a filament electrode E, and a control means CC to control so as to actuate the discharge lamp lighting circuit by an AM dimming method in a region of a lamp current in which a switching point It of the lamp current is larger than a value satisfying a mathematical equation: 0It40Itest (%) (Itest is specific value of filament electrode of discharge lamp), and so as to actuate the discharge lamp lighting circuit by a PWM dimming method in a region of the lamp current in the switching point or less.