To reduce the depth of, facilitate inspection of, and prevent electromagnetic radiation from a lighting device by arranging lighting circuit components located in a holding case attached to a lighting device body on the back side of a discharge bulb socket in the outer peripheral area of the socket.

A headlight for four-lamp arrangement for example is attached to a vehicle body of an automobile using stud bolts 8 located on the back side of a lighting unit body 1. A lighting circuit case 20, since some of starter circuit components are housed in a lower case 22, may be made with a reduced rearward protruding dimension of the back side of the body 1. Namely, overall depth of the headlight may be reduced. Furthermore, in the state of an upper case 21 and the lower case 22 both formed of a metallic material being joined together, since the path in which a high voltage current occurs and flows is shielded, electromagnetic radiation occurring there is shielded. Moreover, inspection of starter circuit and replacement of components housed in the cases may be easily made by removing the lower case 22 from the upper case 21.