Patent ID: 8766879

Claim:
A head-up display apparatus, which projects a display image onto a projection surface of a display member, which is formed as a concave surface, to enable a viewer to view a virtual image of the display image from a predetermined viewing area, the head-up display apparatus comprising: a screen member that includes an imaging surface, on which the display image to be projected onto the projection surface is formed at time of projecting the display image onto the projection surface, wherein the imaging surface is formed as a convex surface that corrects a curvature of field of the virtual image, which is caused by a curvature of the projection surface; a projector that projects a light from a diagonally lower side of the imaging surface to form the display image on the imaging surface; and a focusing point adjusting optical system that includes a free-form-surface lens, which is placed at the diagonally lower side of the imaging surface, wherein: the focusing point adjusting optical system adjusts a focusing point, in which the light projected from the projector is focused, to place the focusing point on the imaging surface; a shape of a light input surface of the free-form-surface lens along a predetermined direction, which is perpendicular to an optical axis of the light entering the light input surface, is defined by a polynomial that includes a cubic term, so that a lower half of the light input surface in the predetermined direction is curved and is protruded toward the projector to focus the light, which passes through the lower half of the light input surface and reaches a lower half of the imaging surface, at a location, which is closer to the projector, and an upper half of the light input surface in the predetermined direction is curved and recessed in a direction away from the projector to focus the light, which passes through the upper half of the light input surface and reaches an upper half of the imaging surface, at a location, which is further away from the projector.