PURPOSE: To display a topographic image on a HUD panel when a pilot gets vertiginous to facilitate the recovery from the vertigo, and improve safety.

CONSTITUTION: The control panel 4 of a HUD has a display mode change-over switch 5 for switching general display mode and urgent display mode. When the urgent display mode is designated by the display mode change-over switch 5 when a pilot gets vertiginous, a HUD digital computer 3 generates a topographic image data which would be seen from the visual point of the pilot on the basis of measurement information such as the speed and altitude of an airframe inputted through an A/D converter 1, the self position information from a highly precise navigation sensor 6, and the topographic data stored in a memory device 7, and displays it on a CRT 8 through a display processor 2. The topographic image displayed on the CRT 8 is projected onto a HUD display panel 11 through a mirror 9 and a lens system 10 to assist the pilot in recovering from the vertigo.