A high beam and a low beam is disclosed, the headlight including: a first light source unit; a second light source unit; a first light output unit; a second light output unit; and a controller configured to adjust a light quantity irradiated from the light source in response to a low beam mode or a high beam mode, and to control a beam output of the first light output unit and the second light output unit by allowing the first optical unit to be arranged selectively on a light path between the light source unit and the second optical unit.