A vehicle headlight device 100 includes a light source 11, a Dove prism 40, and a rotation mechanism 50. The light source 11 emits light. The Dove prism 40 changes a propagation direction of light received at an incidence surface 401 to bring the light to a reflecting surface 402, and changes a propagation direction of light reflected at the reflecting surface 402 to output the light from an exit surface 403. The rotation mechanism 50 rotatably supports the Dove prism 40 about a line which passes through the incidence surface 401 and the exit surface 403 as an axis of rotation R, and rotates the Dove prism 40 in a direction opposite to a bank direction of a vehicle body in accordance with a bank angle k of the vehicle body.