The lighting device of one aspect according to the present disclosure calculates, based on a voltage value of an AC voltage applied to a discharge lamp and a current value of AC current flowing through the discharge lamp, a first power value defined as a value of power supplied to the discharge lamp in a first half period of the AC voltage and a second power value defined as a value of power supplied to the discharge lamp in a second half period of the AC voltage. The lighting device determines that a ground fault has occurred, when an imbalance state in which a difference between the first power value and the second power value is equal to or greater than a threshold value continues for a predetermined time period.