To increase the light utilization efficiency when selective light irradiation is performed using a liquid crystal element (a liquid crystal device). A lamp unit including: a light source; a reflective polarizing plate disposed at a position where light from the light source is incident; a reflecting mirror configured to reflect a reflected light generated by the reflective polarizing plate and re-enters the reflected light to the reflective polarizing plate; a liquid crystal device disposed on the light emitting surface side of the reflective polarizing plate; a polarizing plate disposed on the light emitting surface side of the liquid crystal device; and a lens disposed on the light emitting surface side of the polarizing plate.