Provided is a head-up display apparatus that projects a display image, which is formed on a display surface, onto a projection surface of a movable body to display a virtual image viewable from a cabin of the movable body. The head-up display apparatus includes a display with pixels arranged along the display surface, a light source, and a diffusion plate for diffusing the light coming from the light source and emits the diffused light toward the display. The diffusion plate has through-holes in a thickness direction. In a specific direction on the display surface, an inner dimension of the through-hole is smaller than a pixel pitch of the pixels.