Provided is a light guide plate for an image display device which uses lead-free glass, has excellent color reproducibility and a light weight, and may obtain a wide viewing angle. A light guide plate for an image display device, which guides image light inputted from an image display element and outputs the image light toward a user's pupil, is configured to be made of lead-free glass having a refractive index of 1.8 or more with respect to a wavelength of the image light, and to have internal transmittance of 0.6 or more with respect to a wavelength of 400 nm when a plate thickness is 10 mm.