34 contains Ta2O5 or TiO2 as a primary component, it is not absolutely necessary for the first dielectric film 34 to contain Ta2O5 or TiO2 as a primary component and the first dielectric film 34 may contain an oxide other than Ta2O5 and TiO2 as a primary component. [0234] Moreover, in the above described embodiment, although the second dielectric film 32 is formed of the mixture of ZnS and SiO2, i