A lighting device has a direct-current power generation circuit, a rectangular-wave generation circuit, a pulse generating circuit, lamp-voltage detection means, and pulse-generation command means. The direct-current power generation circuit generates direct-current power from external power. The rectangular-wave generation circuit converts the direct-current power to rectangular-wave alternating-current power. The pulse generating circuit superposes high-voltage pulses on the rectangular-wave power output from the rectangular-wave generation circuit and starts a discharge lamp. The lamp-voltage detection means detects, in digital form, a lamp voltage supplied to the discharge lamp. The pulse-generation command means issues a pulse generation command to the pulse generating circuit when the value detected by the lamp-voltage detection means reaches a predetermined no-load-voltage determination level.