A transparent substrate 2, into which light from a light source 9 is introduced through at least one side, includes a transparent first glass substrate (substrate body) 5a and a low refractive index layer 6 that is disposed on the first glass substrate 5a and has a lower refractive index than the first glass substrate 5a. Moreover, a high refractive index layer 7 having a higher refractive index than the low refractive index layer 6 is disposed on the low refractive index layer 6, thereby preventing the generation of light that leaks from the first glass substrate 5a to the outside through the low refractive index layer 6.