A film structure comprises a substrate and a buffer film formed on the substrate. The substrate is a 36° to 48° rotated Y-cut Si substrate, or the substrate is a SOI substrate including a base substance made of the 36° to 48° rotated Y-cut Si substrate, an insulating layer on the base substance, and a SOI layer made of a Si film on the insulating layer, and a mirror index of a crystal plane of an upper surface of the SOI layer is equal to a mirror index of a crystal plane of an upper surface of the base substance. The buffer film includes ZrO2 epitaxially grown on the substrate.