The head-up display device includes a display element that emits image light and a virtual image optical system. The virtual image optical system includes a lens unit and a free curved surface mirror disposed along the emission direction of the image light in this order from a position close to the display element. The display element is disposed with a tilting attitude with respect to the optical axis of the lens unit with an end on the housing aperture side in an emission surface being close to an incidence surface in the lens unit and with an end on the opposite side of the housing aperture in an emission surface being apart from an incidence surface in the lens unit. The lens unit has an optical characteristic of optically enlarging an optical path length difference according to a virtual image distance difference.