Abstract: A vehicular headlamp employing a discharge bulb as a light source in which a lighting circuit for the bulb, including an ignitor, is secured to a lamp housing in such a manner as to cover a rear opening in the housing. This arrangement results in significantly reduced danger of shock and reduced radiation of electromagnetic noise. In another embodiment of the invention, a lighting-circuit-accommodating unit containing a lighting circuit is bayonet-engaged with a circular opening in the rear wall of a lamp body, and also is fixed to the lamp body by a second fixing device in such a manner as to prevent rotation of the lighting-circuit-accommodating unit relative to the lamp body.