PROJECTION OPTICAL SYSTEM, HEAD-UP DISPLAY DEVICE, AND VEHICLE

A compact head-up display device is provided. For that purpose, the head-up display device includes a projection optical system which includes an image forming unit to display image information and an ocular optical system to reflect light emitted from the image forming unit to display a virtual image. In the ocular optical system, a free-form surface lens and a free-form surface concave mirror are arranged in order from the image forming unit. The shape of the free-form surface concave mirror is such that curvature radius RY in projection on a vertical cross section of the coordinate system of an eye-box is smaller than curvature radius RX in projection on a horizontal cross section.