A head-up display includes: a display that displays an image; and a projection optical system that forms a virtual image. The projection optical system includes: a first mirror disposed above the display that reflects display light of the image; and a second mirror that reflects the display light from the first mirror toward a display medium onto which the virtual image is projected. Moreover, a first expression that defines a sag height at a position (x, y) relative to an axis that defines a plane is satisfied. Moreover, second and third expressions related to variable in the first expression are also satisfied.