An image generating device includes a first light source, a light conversion element, and an image generating element. The first light source is for generating light with a first wavelength. The light conversion element is disposed on a light path of the light with the first wavelength. The light conversion element includes a first quantum dot layer for converting light with wavelengths under a second wavelength to light with the second wavelength, and a second quantum dot layer for converting light with wavelengths under a third wavelength to light with the third wavelength. The first wavelength is smaller than the second wavelength, and the second wavelength is smaller than the third wavelength. The image generating element is for generating images according to light transmitted from the light conversion element.