A lamp unit (500,600,700,800,900) includes a lamp (200) provided with a mirror (60) and a housing (80) for holding the lamp (200) provided with a mirror. The lamp (200) provided with a mirror includes a discharge lamp (100) including a luminous bulb (10) in which a luminous material is enclosed and a pair of electrodes (12,12') are opposed to each other in the luminous bulb (10); and a pair of sealing portions (20,20') for sealing a pair of metal foils (24) electrically connected to the pair of electrodes (12,12'), respectively; and a reflecting mirror (60) for reflecting light emitted from the discharge lamp (100) and having a front opening (60a) for emitting the reflected light. The lamp (200) provided with a mirror (60) is formed so as to have a non-airtight structure. The housing (80) includes a transmission window (70) made of a material for transmitting light emitted from the front opening (60a) and positioned forward in the emission direction (50) of the front opening (60a) of the reflecting mirror (60).