To increase the degree of freedom of the constitution of a projection optical system while keeping the high resolution of the display images of a video display device provided with a display element and the projection optical system forming the optical images of images displayed by the display element.

The video display device is provided with a light source arranged at a position almost conjugate with the pupil of the projection optical system for illuminating the display element and generating a display luminous flux. The light emission diameter of the light source is adjusted so as to make the diameter of effective display luminous fluxes composed of diffracted light within the first order among the display luminous fluxes emitted from the display element smaller than the diameter of the pupil when the luminous fluxes are made incident on the pupil. When the diameter of the effective display luminous fluxes is limited to be small in such a manner, the image is easily formed compared to the time at which it is not limited. That is, the illumination optical system of the video display device increases the degree of freedom of the constitution of an image forming optical system while keeping the resolution of the display image.