There is provided a composite thin film-holding substrate in which a
composite thin film (4) comprising a filler (2) having a refractive index
lower than that of a substrate (1) and a binder (3) having a refractive
index higher than that of the filler (2) is formed on a surface of the
substrate (1). Light is efficiently scattered when passing through the
composite thin film (3) which comprises the filler (2) and the binder (3)
having different refractive indexes from each other. In addition, the
refractive index of a composite thin film (4) comprising a filler (2)
having a low refractive index is low. As a result, the discharge
efficiency of light which passes through the composite thin film (4) from
the substrate (1) to the external is improved.