A method for runtime environment emulation involves loading an application class of an object-oriented application, where the object-oriented application is executing in a runtime environment, and where the application class includes a method call that is unsupported by the runtime environment. A bottom insulating film includes a dielectric film that exhibits a FN type electroconductivity and makes the energy barrier between the bottom insulating film and the substrate lower than that between silicon dioxide and silicon. The rear plate is fixed to the main frame at least at three separate positions, at least one position being offset from a hypothetical line connecting the other two positions.