A discharge bulb is provided with an arc tube main body in which an arc
tube having a discharge light emitting portion (a hermetically sealed
glass envelope) where electrodes are provided in such a manner as to face
each other is enclosed in a cylindrical shroud glass tube. The discharge
bulb is configured so that a light distribution pattern having a
predetermined cut-off line is formed by light intercepting portions
(light intercepting films) and a light distribution control reflector. A
frost treatment is applied to only a light emitting area on an outer
surface of the shroud glass tube which corresponds to an area along the
cut-off line in the light distribution pattern.