To provide a lamp unit which is equipped with a heat radiation cover, making heat radiation of the lamp unit proper, while preventing the fragments of a discharge lamp from scattering.

The lamp unit (10) has the discharge lamp (30) fixed to a reflector (11), by protruding a lamp base (33) to the center backward of an approximately semi-spherical reflector (11), which is provided with the heat radiation cover (50) having a cylindrical cylinder part (51) and the disc-shaped rear end part (53) for closing the rear end of the cylinder part (51) backward of the reflector (11), in which the front end of the heat radiation cover (50) that has opened an aperture at the front; while a hole part (55) is provided at the center of the rear end part (53) is made to contact the outer surface of the reflector (11), and in which the position of the hole part (55) is adjusted to the position of the lamp base (33) that is a lamp electrode and the heat dissipation cover (50) is fixed to the reflector (11) by a cover locking tool (71).