The composite structure of the present invention includes a substrate, and a structure provided on the substrate surface and having a brittle material as the principal component thereof. The structure is polycrystalline, and the average crystallite size is 100 nm or less. The substrate includes at least a first region containing the substrate surface. The first region includes a filler and a matrix which has a first resin as the principal component thereof. The diameter of 90% of the filler particles (D90) is 1.0-60 μm, inclusive. The surface area fill rate of the filler at the substrate surface per unit area is greater than 10% and no greater than 70%.