Display device and light-guiding device

A display device comprising:

• an image light generating device configured to emit image light;
• a first diffraction element of a reflection type configured to deflect the image light incident on a first incident surface toward an eye of an observer;
• and
• a transmission-type second diffraction element disposed in an optical path between the image light generating device and the first diffraction element and configured to deflect the image light incident on a second incident surface toward the first diffraction element, wherein
• the first diffraction element and the second diffraction element are disposed in such a way that,
• when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an even number, a direction in which light incident on the first incident surface is diffracted at the highest diffraction efficiency is the same direction as a direction in which light incident on the second incident surface is diffracted at the highest diffraction efficiency when seen from a normal direction of a virtual surface including a normal direction of the first incident surface and a normal direction of the second incident surface, and
• when a sum of the number of reflections of light and the number of times of generating intermediate image between the second diffraction element and the first diffraction element is an odd number, a direction in which light incident on the first incident surface is diffracted at the highest diffraction efficiency is a direction different from a direction in which light incident on the second incident surface is diffracted at the highest diffraction efficiency when seen from the normal direction of the virtual surface.