Head-up display and mobile body equipped with head-up display and projection optical system

A head-up display of the present disclosure projects a display image on a transparent reflecting member. The head-up display includes: a display device that displays the display image; and a projection optical system that projects the display image displayed on the display device. On an assumption that light reaching a center of a viewpoint region of the observer and corresponding to a center of the virtual image is reference light, the projection optical system includes a prism element that has an incident surface, a reflection surface, and an emitting surface different from the incident surface sequentially in an optical path from the display device. The emitting surface is inclined to the reference light. An inclination amount θ2 of the reference light emitted from the emitting surface with respect to the emitting surface lies in a range of 15°